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mariadb/sql/item_subselect.cc
Oleksandr Byelkin 47e9678982 MDEV-29022 add_slave destroy child list and has dead code 
Nowdays subquery in a UNION's ORDER BY placed correctly in fake select,
the only problem was incorrect Name_resolution_contect is fixed by this
patch in parsing, so we do not need scanning/reseting of ORDER BY of
a union.
2022-09-27 09:56:21 +02:00

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/* Copyright (c) 2002, 2016, Oracle and/or its affiliates.
Copyright (c) 2010, 2021, MariaDB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
/**
@file
@brief
subselect Item
@todo
- add function from mysql_select that use JOIN* as parameter to JOIN
methods (sql_select.h/sql_select.cc)
*/
#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation // gcc: Class implementation
#endif
#include "mariadb.h"
#include "sql_priv.h"
/*
It is necessary to include set_var.h instead of item.h because there
are dependencies on include order for set_var.h and item.h. This
will be resolved later.
*/
#include "sql_class.h" // set_var.h: THD
#include "set_var.h"
#include "sql_select.h"
#include "sql_parse.h" // check_stack_overrun
#include "sql_cte.h"
#include "sql_test.h"
double get_post_group_estimate(JOIN* join, double join_op_rows);
LEX_CSTRING exists_outer_expr_name= { STRING_WITH_LEN("<exists outer expr>") };
int check_and_do_in_subquery_rewrites(JOIN *join);
Item_subselect::Item_subselect(THD *thd_arg):
Item_result_field(thd_arg), Used_tables_and_const_cache(),
value_assigned(0), own_engine(0), thd(0), old_engine(0),
have_to_be_excluded(0),
inside_first_fix_fields(0), done_first_fix_fields(FALSE),
expr_cache(0), forced_const(FALSE), substitution(0), engine(0), eliminated(FALSE),
changed(0), is_correlated(FALSE), with_recursive_reference(0)
{
DBUG_ENTER("Item_subselect::Item_subselect");
DBUG_PRINT("enter", ("this: %p", this));
sortbuffer.str= 0;
#ifndef DBUG_OFF
exec_counter= 0;
#endif
reset();
/*
Item value is NULL if select_result_interceptor didn't change this value
(i.e. some rows will be found returned)
*/
null_value= TRUE;
DBUG_VOID_RETURN;
}
void Item_subselect::init(st_select_lex *select_lex,
select_result_interceptor *result)
{
/*
Please see Item_singlerow_subselect::invalidate_and_restore_select_lex(),
which depends on alterations to the parse tree implemented here.
*/
DBUG_ENTER("Item_subselect::init");
DBUG_PRINT("enter", ("select_lex: %p this: %p",
select_lex, this));
unit= select_lex->master_unit();
if (unit->item)
{
engine= unit->item->engine;
parsing_place= unit->item->parsing_place;
if (unit->item->substype() == EXISTS_SUBS &&
((Item_exists_subselect *)unit->item)->exists_transformed)
{
/* it is permanent transformation of EXISTS to IN */
unit->item= this;
engine->change_result(this, result, FALSE);
}
else
{
/*
Item can be changed in JOIN::prepare while engine in JOIN::optimize
=> we do not copy old_engine here
*/
unit->thd->change_item_tree((Item**)&unit->item, this);
engine->change_result(this, result, TRUE);
}
}
else
{
SELECT_LEX *outer_select= unit->outer_select();
/*
do not take into account expression inside aggregate functions because
they can access original table fields
*/
parsing_place= (outer_select->in_sum_expr ?
NO_MATTER :
outer_select->parsing_place);
if (unit->is_unit_op() && unit->first_select()->next_select())
engine= new subselect_union_engine(unit, result, this);
else
engine= new subselect_single_select_engine(select_lex, result, this);
}
{
SELECT_LEX *upper= unit->outer_select();
if (upper->parsing_place == IN_HAVING)
upper->subquery_in_having= 1;
/* The subquery is an expression cache candidate */
upper->expr_cache_may_be_used[upper->parsing_place]= TRUE;
}
DBUG_PRINT("info", ("engine: %p", engine));
DBUG_VOID_RETURN;
}
st_select_lex *
Item_subselect::get_select_lex()
{
return unit->first_select();
}
void Item_subselect::cleanup()
{
DBUG_ENTER("Item_subselect::cleanup");
Item_result_field::cleanup();
if (old_engine)
{
if (engine)
engine->cleanup();
engine= old_engine;
old_engine= 0;
}
if (engine)
engine->cleanup();
reset();
filesort_buffer.free_sort_buffer();
my_free(sortbuffer.str);
sortbuffer.str= 0;
value_assigned= 0;
expr_cache= 0;
forced_const= FALSE;
DBUG_PRINT("info", ("exec_counter: %d", exec_counter));
#ifndef DBUG_OFF
exec_counter= 0;
#endif
DBUG_VOID_RETURN;
}
void Item_singlerow_subselect::cleanup()
{
DBUG_ENTER("Item_singlerow_subselect::cleanup");
value= 0; row= 0;
Item_subselect::cleanup();
DBUG_VOID_RETURN;
}
void Item_in_subselect::cleanup()
{
DBUG_ENTER("Item_in_subselect::cleanup");
if (left_expr_cache)
{
left_expr_cache->delete_elements();
delete left_expr_cache;
left_expr_cache= NULL;
}
/*
TODO: This breaks the commented assert in add_strategy().
in_strategy&= ~SUBS_STRATEGY_CHOSEN;
*/
first_execution= TRUE;
pushed_cond_guards= NULL;
Item_subselect::cleanup();
DBUG_VOID_RETURN;
}
void Item_allany_subselect::cleanup()
{
/*
The MAX/MIN transformation through injection is reverted through the
change_item_tree() mechanism. Revert the select_lex object of the
query to its initial state.
*/
for (SELECT_LEX *sl= unit->first_select();
sl; sl= sl->next_select())
if (test_set_strategy(SUBS_MAXMIN_INJECTED))
sl->with_sum_func= false;
Item_in_subselect::cleanup();
}
Item_subselect::~Item_subselect()
{
DBUG_ENTER("Item_subselect::~Item_subselect");
DBUG_PRINT("enter", ("this: %p", this));
if (own_engine)
delete engine;
else
engine->cleanup();
engine= NULL;
DBUG_VOID_RETURN;
}
bool
Item_subselect::select_transformer(JOIN *join)
{
DBUG_ENTER("Item_subselect::select_transformer");
DBUG_ASSERT(thd == join->thd);
DBUG_RETURN(false);
}
bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
{
char const *save_where= thd_param->where;
uint8 uncacheable;
bool res;
thd= thd_param;
DBUG_ASSERT(unit->thd == thd);
status_var_increment(thd_param->status_var.feature_subquery);
DBUG_ASSERT(fixed == 0);
engine->set_thd((thd= thd_param));
if (!done_first_fix_fields)
{
done_first_fix_fields= TRUE;
inside_first_fix_fields= TRUE;
upper_refs.empty();
/*
psergey-todo: remove _first_fix_fields calls, we need changes on every
execution
*/
}
eliminated= FALSE;
parent_select= thd_param->lex->current_select;
if (check_stack_overrun(thd, STACK_MIN_SIZE, (uchar*)&res))
return TRUE;
for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
{
if (sl->tvc)
{
if (!(sl= wrap_tvc_into_select(thd, sl)))
{
res= TRUE;
goto end;
}
if (sl == unit->first_select() && !sl->next_select())
unit->fake_select_lex= 0;
}
}
if (!(res= engine->prepare(thd)))
{
// all transformation is done (used by prepared statements)
changed= 1;
inside_first_fix_fields= FALSE;
/*
Substitute the current item with an Item_in_optimizer that was
created by Item_in_subselect::select_in_like_transformer and
call fix_fields for the substituted item which in turn calls
engine->prepare for the subquery predicate.
*/
if (substitution)
{
/*
If the top item of the WHERE/HAVING condition changed,
set correct WHERE/HAVING for PS.
*/
if (unit->outer_select()->where == (*ref))
unit->outer_select()->where= substitution;
else if (unit->outer_select()->having == (*ref))
unit->outer_select()->having= substitution;
(*ref)= substitution;
substitution->name= name;
if (have_to_be_excluded)
engine->exclude();
substitution= 0;
thd->where= "checking transformed subquery";
res= (*ref)->fix_fields_if_needed(thd, ref);
goto end;
}
// Is it one field subselect?
if (engine->cols() > max_columns)
{
my_error(ER_OPERAND_COLUMNS, MYF(0), 1);
res= TRUE;
goto end;
}
if (fix_length_and_dec())
{
res= TRUE;
goto end;
}
}
else
goto end;
if ((uncacheable= engine->uncacheable() & ~UNCACHEABLE_EXPLAIN) ||
with_recursive_reference)
{
const_item_cache= 0;
if (uncacheable & UNCACHEABLE_RAND)
used_tables_cache|= RAND_TABLE_BIT;
}
fixed= 1;
end:
done_first_fix_fields= FALSE;
inside_first_fix_fields= FALSE;
thd->where= save_where;
return res;
}
bool Item_subselect::enumerate_field_refs_processor(void *arg)
{
List_iterator<Ref_to_outside> it(upper_refs);
Ref_to_outside *upper;
while ((upper= it++))
{
if (upper->item &&
upper->item->walk(&Item::enumerate_field_refs_processor, FALSE, arg))
return TRUE;
}
return FALSE;
}
bool Item_subselect::mark_as_eliminated_processor(void *arg)
{
eliminated= TRUE;
return FALSE;
}
/**
Remove a subselect item from its unit so that the unit no longer
represents a subquery.
@param arg unused parameter
@return
FALSE to force the evaluation of the processor for the subsequent items.
*/
bool Item_subselect::eliminate_subselect_processor(void *arg)
{
unit->item= NULL;
if (!unit->is_excluded())
unit->exclude();
eliminated= TRUE;
return FALSE;
}
bool Item_subselect::mark_as_dependent(THD *thd, st_select_lex *select,
Item *item)
{
if (inside_first_fix_fields)
{
is_correlated= TRUE;
Ref_to_outside *upper;
if (!(upper= new (thd->stmt_arena->mem_root) Ref_to_outside()))
return TRUE;
upper->select= select;
upper->item= item;
if (upper_refs.push_back(upper, thd->stmt_arena->mem_root))
return TRUE;
}
return FALSE;
}
/*
@brief
Update the table bitmaps for the outer references used within a subquery
*/
bool Item_subselect::update_table_bitmaps_processor(void *arg)
{
List_iterator<Ref_to_outside> it(upper_refs);
Ref_to_outside *upper;
while ((upper= it++))
{
if (upper->item &&
upper->item->walk(&Item::update_table_bitmaps_processor, FALSE, arg))
return TRUE;
}
return FALSE;
}
/*
Adjust attributes after our parent select has been merged into grandparent
DESCRIPTION
Subquery is a composite object which may be correlated, that is, it may
have
1. references to tables of the parent select (i.e. one that has the clause
with the subquery predicate)
2. references to tables of the grandparent select
3. references to tables of further ancestors.
Before the pullout, this item indicates:
- #1 with table bits in used_tables()
- #2 and #3 with OUTER_REF_TABLE_BIT.
After parent has been merged with grandparent:
- references to parent and grandparent tables should be indicated with
table bits.
- references to greatgrandparent and further ancestors - with
OUTER_REF_TABLE_BIT.
*/
void Item_subselect::fix_after_pullout(st_select_lex *new_parent,
Item **ref, bool merge)
{
recalc_used_tables(new_parent, TRUE);
parent_select= new_parent;
}
class Field_fixer: public Field_enumerator
{
public:
table_map used_tables; /* Collect used_tables here */
st_select_lex *new_parent; /* Select we're in */
virtual void visit_field(Item_field *item)
{
//for (TABLE_LIST *tbl= new_parent->leaf_tables; tbl; tbl= tbl->next_local)
//{
// if (tbl->table == field->table)
// {
used_tables|= item->field->table->map;
// return;
// }
//}
//used_tables |= OUTER_REF_TABLE_BIT;
}
};
/*
Recalculate used_tables_cache
*/
void Item_subselect::recalc_used_tables(st_select_lex *new_parent,
bool after_pullout)
{
List_iterator_fast<Ref_to_outside> it(upper_refs);
Ref_to_outside *upper;
DBUG_ENTER("recalc_used_tables");
used_tables_cache= 0;
while ((upper= it++))
{
bool found= FALSE;
/*
Check if
1. the upper reference refers to the new immediate parent select, or
2. one of the further ancestors.
We rely on the fact that the tree of selects is modified by some kind of
'flattening', i.e. a process where child selects are merged into their
parents.
The merged selects are removed from the select tree but keep pointers to
their parents.
*/
for (st_select_lex *sel= upper->select; sel; sel= sel->outer_select())
{
/*
If we've reached the new parent select by walking upwards from
reference's original select, this means that the reference is now
referring to the direct parent:
*/
if (sel == new_parent)
{
found= TRUE;
/*
upper->item may be NULL when we've referred to a grouping function,
in which case we don't care about what it's table_map really is,
because item->with_sum_func==1 will ensure correct placement of the
item.
*/
if (upper->item)
{
// Now, iterate over fields and collect used_tables() attribute:
Field_fixer fixer;
fixer.used_tables= 0;
fixer.new_parent= new_parent;
upper->item->walk(&Item::enumerate_field_refs_processor, 0, &fixer);
used_tables_cache |= fixer.used_tables;
upper->item->walk(&Item::update_table_bitmaps_processor, FALSE, NULL);
/*
if (after_pullout)
upper->item->fix_after_pullout(new_parent, &(upper->item));
upper->item->update_used_tables();
*/
}
}
}
if (!found)
used_tables_cache|= OUTER_REF_TABLE_BIT;
}
/*
Don't update const_tables_cache yet as we don't yet know which of the
parent's tables are constant. Parent will call update_used_tables() after
he has done const table detection, and that will be our chance to update
const_tables_cache.
*/
DBUG_PRINT("exit", ("used_tables_cache: %llx", used_tables_cache));
DBUG_VOID_RETURN;
}
/**
Determine if a subquery is expensive to execute during query optimization.
@details The cost of execution of a subquery is estimated based on an
estimate of the number of rows the subquery will access during execution.
This measure is used instead of JOIN::read_time, because it is considered
to be much more reliable than the cost estimate.
@return true if the subquery is expensive
@return false otherwise
*/
bool Item_subselect::is_expensive()
{
double examined_rows= 0;
bool all_are_simple= true;
/* check extremely simple select */
if (!unit->first_select()->next_select()) // no union
{
/*
such single selects works even without optimization because
can not makes loops
*/
SELECT_LEX *sl= unit->first_select();
JOIN *join = sl->join;
if (join && !join->tables_list && !sl->first_inner_unit())
return false;
}
for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
{
JOIN *cur_join= sl->join;
/* not optimized subquery */
if (!cur_join)
return true;
/*
If the subquery is not optimised or in the process of optimization
it supposed to be expensive
*/
if (cur_join->optimization_state != JOIN::OPTIMIZATION_DONE)
return true;
if (!cur_join->tables_list && !sl->first_inner_unit())
continue;
/*
Subqueries whose result is known after optimization are not expensive.
Such subqueries have all tables optimized away, thus have no join plan.
*/
if ((cur_join->zero_result_cause || !cur_join->tables_list))
continue;
/*
This is not simple SELECT in union so we can not go by simple condition
*/
all_are_simple= false;
/*
If a subquery is not optimized we cannot estimate its cost. A subquery is
considered optimized if it has a join plan.
*/
if (!cur_join->join_tab)
return true;
if (sl->first_inner_unit())
{
/*
Subqueries that contain subqueries are considered expensive.
@todo: accumulate the cost of subqueries.
*/
return true;
}
examined_rows+= cur_join->get_examined_rows();
}
// here we are sure that subquery is optimized so thd is set
return !all_are_simple &&
(examined_rows > thd->variables.expensive_subquery_limit);
}
static
int walk_items_for_table_list(Item_processor processor,
bool walk_subquery, void *argument,
List<TABLE_LIST>& join_list)
{
List_iterator<TABLE_LIST> li(join_list);
int res;
while (TABLE_LIST *table= li++)
{
if (table->on_expr)
{
if ((res= table->on_expr->walk(processor, walk_subquery, argument)))
return res;
}
if (table->nested_join)
{
if ((res= walk_items_for_table_list(processor, walk_subquery, argument,
table->nested_join->join_list)))
return res;
}
}
return 0;
}
bool Item_subselect::walk(Item_processor processor, bool walk_subquery,
void *argument)
{
if (!(unit->uncacheable & ~UNCACHEABLE_DEPENDENT) && engine->is_executed() &&
!unit->describe)
{
/*
The subquery has already been executed (for real, it wasn't EXPLAIN's
fake execution) so it should not matter what it has inside.
The actual reason for not walking inside is that parts of the subquery
(e.g. JTBM join nests and their IN-equality conditions may have been
invalidated by irreversible cleanups (those happen after an uncorrelated
subquery has been executed).
*/
return (this->*processor)(argument);
}
if (walk_subquery)
{
for (SELECT_LEX *lex= unit->first_select(); lex; lex= lex->next_select())
{
List_iterator<Item> li(lex->item_list);
Item *item;
ORDER *order;
if (lex->where && (lex->where)->walk(processor, walk_subquery, argument))
return 1;
if (lex->having && (lex->having)->walk(processor, walk_subquery,
argument))
return 1;
if (walk_items_for_table_list(processor, walk_subquery, argument,
*lex->join_list))
return 1;
while ((item=li++))
{
if (item->walk(processor, walk_subquery, argument))
return 1;
}
for (order= lex->order_list.first ; order; order= order->next)
{
if ((*order->item)->walk(processor, walk_subquery, argument))
return 1;
}
for (order= lex->group_list.first ; order; order= order->next)
{
if ((*order->item)->walk(processor, walk_subquery, argument))
return 1;
}
}
}
return (this->*processor)(argument);
}
bool Item_subselect::exec()
{
subselect_engine *org_engine= engine;
DBUG_ENTER("Item_subselect::exec");
DBUG_ASSERT(fixed);
DBUG_ASSERT(!eliminated);
DBUG_EXECUTE_IF("Item_subselect",
Item::Print print(this,
enum_query_type(QT_TO_SYSTEM_CHARSET |
QT_WITHOUT_INTRODUCERS));
push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
ER_UNKNOWN_ERROR, "DBUG: Item_subselect::exec %.*s",
print.length(),print.ptr());
);
/*
Do not execute subselect in case of a fatal error
or if the query has been killed.
*/
if (unlikely(thd->is_error() || thd->killed))
DBUG_RETURN(true);
DBUG_ASSERT(!thd->lex->context_analysis_only);
/*
Simulate a failure in sub-query execution. Used to test e.g.
out of memory or query being killed conditions.
*/
DBUG_EXECUTE_IF("subselect_exec_fail", DBUG_RETURN(true););
bool res= engine->exec();
#ifndef DBUG_OFF
++exec_counter;
#endif
if (engine != org_engine)
{
/*
If the subquery engine changed during execution due to lazy subquery
optimization, or because the original engine found a more efficient other
engine, re-execute the subquery with the new engine.
*/
DBUG_RETURN(exec());
}
DBUG_RETURN(res);
}
void Item_subselect::get_cache_parameters(List<Item> &parameters)
{
Collect_deps_prm prm= {&parameters, // parameters
unit->first_select()->nest_level_base, // nest_level_base
0, // count
unit->first_select()->nest_level, // nest_level
TRUE // collect
};
walk(&Item::collect_outer_ref_processor, TRUE, &prm);
}
int Item_in_subselect::optimize(double *out_rows, double *cost)
{
int res;
DBUG_ENTER("Item_in_subselect::optimize");
DBUG_ASSERT(fixed);
SELECT_LEX *save_select= thd->lex->current_select;
JOIN *join= unit->first_select()->join;
thd->lex->current_select= join->select_lex;
if ((res= join->optimize()))
DBUG_RETURN(res);
/* Calculate #rows and cost of join execution */
join->get_partial_cost_and_fanout(join->table_count - join->const_tables,
table_map(-1),
cost, out_rows);
/*
Adjust join output cardinality. There can be these cases:
- Have no GROUP BY and no aggregate funcs: we won't get into this
function because such join will be processed as a merged semi-join
(TODO: does it really mean we don't need to handle such cases here at
all? put ASSERT)
- Have no GROUP BY but have aggregate funcs: output is 1 record.
- Have GROUP BY and have (or not) aggregate funcs: need to adjust output
cardinality.
*/
thd->lex->current_select= save_select;
if (!join->group_list && !join->group_optimized_away &&
join->tmp_table_param.sum_func_count)
{
DBUG_PRINT("info",("Materialized join will have only 1 row (it has "
"aggregates but no GROUP BY"));
*out_rows= 1;
}
/* Now with grouping */
if (join->group_list_for_estimates)
{
DBUG_PRINT("info",("Materialized join has grouping, trying to estimate it"));
double output_rows= get_post_group_estimate(join, *out_rows);
DBUG_PRINT("info",("Got value of %g", output_rows));
*out_rows= output_rows;
}
DBUG_RETURN(res);
}
/**
Check if an expression cache is needed for this subquery
@param thd Thread handle
@details
The function checks whether a cache is needed for a subquery and whether
the result of the subquery can be put in cache.
@retval TRUE cache is needed
@retval FALSE otherwise
*/
bool Item_subselect::expr_cache_is_needed(THD *thd)
{
return ((engine->uncacheable() & UNCACHEABLE_DEPENDENT) &&
engine->cols() == 1 &&
optimizer_flag(thd, OPTIMIZER_SWITCH_SUBQUERY_CACHE) &&
!(engine->uncacheable() & (UNCACHEABLE_RAND |
UNCACHEABLE_SIDEEFFECT)) &&
!with_recursive_reference);
}
/**
Check if the left IN argument contains NULL values.
@retval TRUE there are NULLs
@retval FALSE otherwise
*/
inline bool Item_in_subselect::left_expr_has_null()
{
return (*(optimizer->get_cache()))->null_value_inside;
}
/**
Check if an expression cache is needed for this subquery
@param thd Thread handle
@details
The function checks whether a cache is needed for a subquery and whether
the result of the subquery can be put in cache.
@note
This method allows many columns in the subquery because it is supported by
Item_in_optimizer and result of the IN subquery will be scalar in this
case.
@retval TRUE cache is needed
@retval FALSE otherwise
*/
bool Item_in_subselect::expr_cache_is_needed(THD *thd)
{
return (optimizer_flag(thd, OPTIMIZER_SWITCH_SUBQUERY_CACHE) &&
!(engine->uncacheable() & (UNCACHEABLE_RAND |
UNCACHEABLE_SIDEEFFECT)) &&
!with_recursive_reference);
}
/*
Compute the IN predicate if the left operand's cache changed.
*/
bool Item_in_subselect::exec()
{
DBUG_ENTER("Item_in_subselect::exec");
DBUG_ASSERT(fixed);
/*
Initialize the cache of the left predicate operand. This has to be done as
late as now, because Cached_item directly contains a resolved field (not
an item, and in some cases (when temp tables are created), these fields
end up pointing to the wrong field. One solution is to change Cached_item
to not resolve its field upon creation, but to resolve it dynamically
from a given Item_ref object.
TODO: the cache should be applied conditionally based on:
- rules - e.g. only if the left operand is known to be ordered, and/or
- on a cost-based basis, that takes into account the cost of a cache
lookup, the cache hit rate, and the savings per cache hit.
*/
if (!left_expr_cache && (test_strategy(SUBS_MATERIALIZATION)))
init_left_expr_cache();
/*
If the new left operand is already in the cache, reuse the old result.
Use the cached result only if this is not the first execution of IN
because the cache is not valid for the first execution.
*/
if (!first_execution && left_expr_cache &&
test_if_item_cache_changed(*left_expr_cache) < 0)
DBUG_RETURN(FALSE);
/*
The exec() method below updates item::value, and item::null_value, thus if
we don't call it, the next call to item::val_int() will return whatever
result was computed by its previous call.
*/
DBUG_RETURN(Item_subselect::exec());
}
Item::Type Item_subselect::type() const
{
return SUBSELECT_ITEM;
}
bool Item_subselect::fix_length_and_dec()
{
if (engine->fix_length_and_dec(0))
return TRUE;
return FALSE;
}
table_map Item_subselect::used_tables() const
{
return (table_map) ((engine->uncacheable() & ~UNCACHEABLE_EXPLAIN)?
used_tables_cache : 0L);
}
bool Item_subselect::const_item() const
{
DBUG_ASSERT(thd);
return (thd->lex->context_analysis_only || with_recursive_reference ?
FALSE :
forced_const || const_item_cache);
}
Item *Item_subselect::get_tmp_table_item(THD *thd_arg)
{
if (!with_sum_func && !const_item())
return new (thd->mem_root) Item_temptable_field(thd_arg, result_field);
return copy_or_same(thd_arg);
}
void Item_subselect::update_used_tables()
{
if (!forced_const)
{
recalc_used_tables(parent_select, FALSE);
if (!(engine->uncacheable() & ~UNCACHEABLE_EXPLAIN))
{
// did all used tables become static?
if (!(used_tables_cache & ~engine->upper_select_const_tables()) &&
! with_recursive_reference)
const_item_cache= 1;
}
}
}
void Item_subselect::print(String *str, enum_query_type query_type)
{
if (query_type & QT_ITEM_SUBSELECT_ID_ONLY)
{
str->append(STRING_WITH_LEN("(subquery#"));
if (unit && unit->first_select())
{
char buf[64];
ll2str(unit->first_select()->select_number, buf, 10, 0);
str->append(buf);
}
else
str->append("NULL"); // TODO: what exactly does this mean?
str->append(")");
return;
}
if (engine)
{
str->append('(');
engine->print(str, query_type);
str->append(')');
}
else
str->append("(...)");
}
Item_singlerow_subselect::Item_singlerow_subselect(THD *thd, st_select_lex *select_lex):
Item_subselect(thd), value(0)
{
DBUG_ENTER("Item_singlerow_subselect::Item_singlerow_subselect");
init(select_lex, new (thd->mem_root) select_singlerow_subselect(thd, this));
maybe_null= 1;
max_columns= UINT_MAX;
DBUG_VOID_RETURN;
}
st_select_lex *
Item_singlerow_subselect::invalidate_and_restore_select_lex()
{
DBUG_ENTER("Item_singlerow_subselect::invalidate_and_restore_select_lex");
st_select_lex *result= get_select_lex();
DBUG_ASSERT(result);
/*
This code restore the parse tree in it's state before the execution of
Item_singlerow_subselect::Item_singlerow_subselect(),
and in particular decouples this object from the SELECT_LEX,
so that the SELECT_LEX can be used with a different flavor
or Item_subselect instead, as part of query rewriting.
*/
unit->item= NULL;
DBUG_RETURN(result);
}
Item_maxmin_subselect::Item_maxmin_subselect(THD *thd,
Item_subselect *parent,
st_select_lex *select_lex,
bool max_arg):
Item_singlerow_subselect(thd), was_values(TRUE)
{
DBUG_ENTER("Item_maxmin_subselect::Item_maxmin_subselect");
max= max_arg;
init(select_lex,
new (thd->mem_root) select_max_min_finder_subselect(thd,
this, max_arg, parent->substype() == Item_subselect::ALL_SUBS));
max_columns= 1;
maybe_null= 1;
max_columns= 1;
/*
Following information was collected during performing fix_fields()
of Items belonged to subquery, which will be not repeated
*/
used_tables_cache= parent->get_used_tables_cache();
const_item_cache= parent->const_item();
DBUG_VOID_RETURN;
}
void Item_maxmin_subselect::cleanup()
{
DBUG_ENTER("Item_maxmin_subselect::cleanup");
Item_singlerow_subselect::cleanup();
/*
By default it is TRUE to avoid TRUE reporting by
Item_func_not_all/Item_func_nop_all if this item was never called.
Engine exec() set it to FALSE by reset_value_registration() call.
select_max_min_finder_subselect::send_data() set it back to TRUE if some
value will be found.
*/
was_values= TRUE;
DBUG_VOID_RETURN;
}
void Item_maxmin_subselect::print(String *str, enum_query_type query_type)
{
str->append(max?"<max>":"<min>", 5);
Item_singlerow_subselect::print(str, query_type);
}
void Item_maxmin_subselect::no_rows_in_result()
{
/*
Subquery predicates outside of the SELECT list must be evaluated in order
to possibly filter the special result row generated for implicit grouping
if the subquery is in the HAVING clause.
If the predicate is constant, we need its actual value in the only result
row for queries with implicit grouping.
*/
if (parsing_place != SELECT_LIST || const_item())
return;
value= (new (thd->mem_root) Item_null(thd))->get_cache(thd);
null_value= 0;
was_values= 0;
make_const();
}
void Item_singlerow_subselect::no_rows_in_result()
{
/*
Subquery predicates outside of the SELECT list must be evaluated in order
to possibly filter the special result row generated for implicit grouping
if the subquery is in the HAVING clause.
If the predicate is constant, we need its actual value in the only result
row for queries with implicit grouping.
*/
if (parsing_place != SELECT_LIST || const_item())
return;
value= (new (thd->mem_root) Item_null(thd))->get_cache(thd);
reset();
make_const();
}
void Item_singlerow_subselect::reset()
{
Item_subselect::reset();
if (value)
{
for(uint i= 0; i < engine->cols(); i++)
row[i]->set_null();
}
}
/**
@todo
- We can't change name of Item_field or Item_ref, because it will
prevent its correct resolving, but we should save name of
removed item => we do not make optimization if top item of
list is field or reference.
- switch off this optimization for prepare statement,
because we do not rollback these changes.
Make rollback for it, or special name resolving mode in 5.0.
@param join Join object of the subquery (i.e. 'child' join).
@retval false The subquery was transformed
*/
bool
Item_singlerow_subselect::select_transformer(JOIN *join)
{
DBUG_ENTER("Item_singlerow_subselect::select_transformer");
if (changed)
DBUG_RETURN(false);
DBUG_ASSERT(join->thd == thd);
SELECT_LEX *select_lex= join->select_lex;
Query_arena *arena= thd->stmt_arena;
if (!select_lex->master_unit()->is_unit_op() &&
!select_lex->table_list.elements &&
select_lex->item_list.elements == 1 &&
!select_lex->item_list.head()->with_sum_func &&
/*
We can't change name of Item_field or Item_ref, because it will
prevent its correct resolving, but we should save name of
removed item => we do not make optimization if top item of
list is field or reference.
TODO: solve above problem
*/
!(select_lex->item_list.head()->type() == FIELD_ITEM ||
select_lex->item_list.head()->type() == REF_ITEM) &&
!join->conds && !join->having &&
/*
switch off this optimization for prepare statement,
because we do not rollback this changes
TODO: make rollback for it, or special name resolving mode in 5.0.
*/
!arena->is_stmt_prepare_or_first_sp_execute()
)
{
have_to_be_excluded= 1;
if (thd->lex->describe)
{
char warn_buff[MYSQL_ERRMSG_SIZE];
sprintf(warn_buff, ER_THD(thd, ER_SELECT_REDUCED),
select_lex->select_number);
push_warning(thd, Sql_condition::WARN_LEVEL_NOTE,
ER_SELECT_REDUCED, warn_buff);
}
substitution= select_lex->item_list.head();
/*
as far as we moved content to upper level we have to fix dependences & Co
*/
substitution->fix_after_pullout(select_lex->outer_select(),
&substitution, TRUE);
}
DBUG_RETURN(false);
}
void Item_singlerow_subselect::store(uint i, Item *item)
{
row[i]->store(item);
row[i]->cache_value();
}
const Type_handler *Item_singlerow_subselect::type_handler() const
{
return engine->type_handler();
}
bool Item_singlerow_subselect::fix_length_and_dec()
{
if ((max_columns= engine->cols()) == 1)
{
if (engine->fix_length_and_dec(row= &value))
return TRUE;
}
else
{
if (!(row= (Item_cache**) current_thd->alloc(sizeof(Item_cache*) *
max_columns)) ||
engine->fix_length_and_dec(row))
return TRUE;
value= *row;
}
unsigned_flag= value->unsigned_flag;
/*
If the subquery has no tables (1) and is not a UNION (2), like:
(SELECT subq_value)
then its NULLability is the same as subq_value's NULLability.
(1): A subquery that uses a table will return NULL when the table is empty.
(2): A UNION subquery will return NULL if it produces a "Subquery returns
more than one row" error.
*/
if (engine->no_tables() &&
engine->engine_type() != subselect_engine::UNION_ENGINE)
maybe_null= engine->may_be_null();
else
{
for (uint i= 0; i < max_columns; i++)
row[i]->maybe_null= TRUE;
}
return FALSE;
}
/**
Add an expression cache for this subquery if it is needed
@param thd_arg Thread handle
@details
The function checks whether an expression cache is needed for this item
and if if so wraps the item into an item of the class
Item_cache_wrapper with an appropriate expression cache set up there.
@note
used from Item::transform()
@return
new wrapper item if an expression cache is needed,
this item - otherwise
*/
Item* Item_singlerow_subselect::expr_cache_insert_transformer(THD *tmp_thd,
uchar *unused)
{
DBUG_ENTER("Item_singlerow_subselect::expr_cache_insert_transformer");
DBUG_ASSERT(thd == tmp_thd);
/*
Do not create subquery cache if the subquery was eliminated.
The optimizer may eliminate subquery items (see
eliminate_subselect_processor). However it does not update
all query's data structures, so the eliminated item may be
still reachable.
*/
if (eliminated)
DBUG_RETURN(this);
if (expr_cache)
DBUG_RETURN(expr_cache);
if (expr_cache_is_needed(tmp_thd) &&
(expr_cache= set_expr_cache(tmp_thd)))
{
init_expr_cache_tracker(tmp_thd);
DBUG_RETURN(expr_cache);
}
DBUG_RETURN(this);
}
uint Item_singlerow_subselect::cols() const
{
return engine->cols();
}
bool Item_singlerow_subselect::check_cols(uint c)
{
if (c != engine->cols())
{
my_error(ER_OPERAND_COLUMNS, MYF(0), c);
return 1;
}
return 0;
}
bool Item_singlerow_subselect::null_inside()
{
for (uint i= 0; i < max_columns ; i++)
{
if (row[i]->null_value)
return 1;
}
return 0;
}
void Item_singlerow_subselect::bring_value()
{
if (!exec() && assigned())
{
null_value= true;
for (uint i= 0; i < max_columns ; i++)
{
if (!row[i]->null_value)
{
null_value= false;
return;
}
}
}
else
reset();
}
double Item_singlerow_subselect::val_real()
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
return value->val_real();
if (!exec() && !value->null_value)
{
null_value= FALSE;
return value->val_real();
}
else
{
reset();
return 0;
}
}
longlong Item_singlerow_subselect::val_int()
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
{
longlong val= value->val_int();
null_value= value->null_value;
return val;
}
if (!exec() && !value->null_value)
{
null_value= FALSE;
return value->val_int();
}
else
{
reset();
DBUG_ASSERT(null_value);
return 0;
}
}
String *Item_singlerow_subselect::val_str(String *str)
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
{
String *res= value->val_str(str);
null_value= value->null_value;
return res;
}
if (!exec() && !value->null_value)
{
null_value= FALSE;
return value->val_str(str);
}
else
{
reset();
DBUG_ASSERT(null_value);
return 0;
}
}
my_decimal *Item_singlerow_subselect::val_decimal(my_decimal *decimal_value)
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
{
my_decimal *val= value->val_decimal(decimal_value);
null_value= value->null_value;
return val;
}
if (!exec() && !value->null_value)
{
null_value= FALSE;
return value->val_decimal(decimal_value);
}
else
{
reset();
DBUG_ASSERT(null_value);
return 0;
}
}
bool Item_singlerow_subselect::val_bool()
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
{
bool val= value->val_bool();
null_value= value->null_value;
return val;
}
if (!exec() && !value->null_value)
{
null_value= FALSE;
return value->val_bool();
}
else
{
reset();
DBUG_ASSERT(null_value);
return 0;
}
}
bool Item_singlerow_subselect::get_date(MYSQL_TIME *ltime,ulonglong fuzzydate)
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
{
bool val= value->get_date(ltime, fuzzydate);
null_value= value->null_value;
return val;
}
if (!exec() && !value->null_value)
{
null_value= FALSE;
return value->get_date(ltime, fuzzydate);
}
else
{
reset();
DBUG_ASSERT(null_value);
return 1;
}
}
Item_exists_subselect::Item_exists_subselect(THD *thd,
st_select_lex *select_lex):
Item_subselect(thd), upper_not(NULL), abort_on_null(0),
emb_on_expr_nest(NULL), optimizer(0), exists_transformed(0)
{
DBUG_ENTER("Item_exists_subselect::Item_exists_subselect");
init(select_lex, new (thd->mem_root) select_exists_subselect(thd, this));
max_columns= UINT_MAX;
null_value= FALSE; //can't be NULL
maybe_null= 0; //can't be NULL
value= 0;
DBUG_VOID_RETURN;
}
void Item_exists_subselect::print(String *str, enum_query_type query_type)
{
str->append(STRING_WITH_LEN("exists"));
Item_subselect::print(str, query_type);
}
bool Item_in_subselect::test_limit(st_select_lex_unit *unit_arg)
{
if (unlikely(unit_arg->fake_select_lex &&
unit_arg->fake_select_lex->test_limit()))
return(1);
SELECT_LEX *sl= unit_arg->first_select();
for (; sl; sl= sl->next_select())
{
if (unlikely(sl->test_limit()))
return(1);
}
return(0);
}
Item_in_subselect::Item_in_subselect(THD *thd, Item * left_exp,
st_select_lex *select_lex):
Item_exists_subselect(thd), left_expr_cache(0), first_execution(TRUE),
in_strategy(SUBS_NOT_TRANSFORMED),
pushed_cond_guards(NULL), do_not_convert_to_sj(FALSE), is_jtbm_merged(FALSE),
is_jtbm_const_tab(FALSE), is_flattenable_semijoin(FALSE),
is_registered_semijoin(FALSE),
upper_item(0),
converted_from_in_predicate(FALSE)
{
DBUG_ENTER("Item_in_subselect::Item_in_subselect");
DBUG_PRINT("info", ("in_strategy: %u", (uint)in_strategy));
left_expr_orig= left_expr= left_exp;
/* prepare to possible disassembling the item in convert_subq_to_sj() */
if (left_exp->type() == Item::ROW_ITEM)
left_expr_orig= new (thd->mem_root)
Item_row(thd, static_cast<Item_row*>(left_exp));
func= &eq_creator;
init(select_lex, new (thd->mem_root) select_exists_subselect(thd, this));
max_columns= UINT_MAX;
maybe_null= 1;
reset();
//if test_limit will fail then error will be reported to client
test_limit(select_lex->master_unit());
DBUG_VOID_RETURN;
}
int Item_in_subselect::get_identifier()
{
return engine->get_identifier();
}
Item_allany_subselect::Item_allany_subselect(THD *thd, Item * left_exp,
chooser_compare_func_creator fc,
st_select_lex *select_lex,
bool all_arg):
Item_in_subselect(thd), func_creator(fc), all(all_arg)
{
DBUG_ENTER("Item_allany_subselect::Item_allany_subselect");
left_expr_orig= left_expr= left_exp;
/* prepare to possible disassembling the item in convert_subq_to_sj() */
if (left_exp->type() == Item::ROW_ITEM)
left_expr_orig= new (thd->mem_root)
Item_row(thd, static_cast<Item_row*>(left_exp));
func= func_creator(all_arg);
init(select_lex, new (thd->mem_root) select_exists_subselect(thd, this));
max_columns= 1;
abort_on_null= 0;
reset();
//if test_limit will fail then error will be reported to client
test_limit(select_lex->master_unit());
DBUG_VOID_RETURN;
}
/**
Initialize length and decimals for EXISTS and inherited (IN/ALL/ANY)
subqueries
*/
void Item_exists_subselect::init_length_and_dec()
{
decimals= 0;
max_length= 1;
max_columns= engine->cols();
}
bool Item_exists_subselect::fix_length_and_dec()
{
DBUG_ENTER("Item_exists_subselect::fix_length_and_dec");
init_length_and_dec();
// If limit is not set or it is constant more than 1
if (!unit->global_parameters()->select_limit ||
(unit->global_parameters()->select_limit->basic_const_item() &&
unit->global_parameters()->select_limit->val_int() > 1))
{
/*
We need only 1 row to determine existence (i.e. any EXISTS that is not
an IN always requires LIMIT 1)
*/
Item *item= new (thd->mem_root) Item_int(thd, (int32) 1);
if (!item)
DBUG_RETURN(TRUE);
thd->change_item_tree(&unit->global_parameters()->select_limit,
item);
unit->global_parameters()->explicit_limit= 1; // we set the limit
DBUG_PRINT("info", ("Set limit to 1"));
}
DBUG_RETURN(FALSE);
}
bool Item_in_subselect::fix_length_and_dec()
{
DBUG_ENTER("Item_in_subselect::fix_length_and_dec");
init_length_and_dec();
/*
Unlike Item_exists_subselect, LIMIT 1 is set later for
Item_in_subselect, depending on the chosen strategy.
*/
DBUG_RETURN(FALSE);
}
/**
Add an expression cache for this subquery if it is needed
@param thd_arg Thread handle
@details
The function checks whether an expression cache is needed for this item
and if if so wraps the item into an item of the class
Item_cache_wrapper with an appropriate expression cache set up there.
@note
used from Item::transform()
@return
new wrapper item if an expression cache is needed,
this item - otherwise
*/
Item* Item_exists_subselect::expr_cache_insert_transformer(THD *tmp_thd,
uchar *unused)
{
DBUG_ENTER("Item_exists_subselect::expr_cache_insert_transformer");
DBUG_ASSERT(thd == tmp_thd);
if (expr_cache)
DBUG_RETURN(expr_cache);
if (substype() == EXISTS_SUBS && expr_cache_is_needed(tmp_thd) &&
(expr_cache= set_expr_cache(tmp_thd)))
{
init_expr_cache_tracker(tmp_thd);
DBUG_RETURN(expr_cache);
}
DBUG_RETURN(this);
}
void Item_exists_subselect::no_rows_in_result()
{
/*
Subquery predicates outside of the SELECT list must be evaluated in order
to possibly filter the special result row generated for implicit grouping
if the subquery is in the HAVING clause.
If the predicate is constant, we need its actual value in the only result
row for queries with implicit grouping.
*/
if (parsing_place != SELECT_LIST || const_item())
return;
value= 0;
null_value= 0;
make_const();
}
double Item_exists_subselect::val_real()
{
DBUG_ASSERT(fixed == 1);
if (!forced_const && exec())
{
reset();
return 0;
}
return (double) value;
}
longlong Item_exists_subselect::val_int()
{
DBUG_ASSERT(fixed == 1);
if (!forced_const && exec())
{
reset();
return 0;
}
return value;
}
/**
Return the result of EXISTS as a string value
Converts the true/false result into a string value.
Note that currently this cannot be NULL, so if the query execution fails
it will return 0.
@param decimal_value[out] buffer to hold the resulting string value
@retval Pointer to the converted string.
Can't be a NULL pointer, as currently
EXISTS cannot return NULL.
*/
String *Item_exists_subselect::val_str(String *str)
{
DBUG_ASSERT(fixed == 1);
if (!forced_const && exec())
reset();
str->set((ulonglong)value,&my_charset_bin);
return str;
}
/**
Return the result of EXISTS as a decimal value
Converts the true/false result into a decimal value.
Note that currently this cannot be NULL, so if the query execution fails
it will return 0.
@param decimal_value[out] Buffer to hold the resulting decimal value
@retval Pointer to the converted decimal.
Can't be a NULL pointer, as currently
EXISTS cannot return NULL.
*/
my_decimal *Item_exists_subselect::val_decimal(my_decimal *decimal_value)
{
DBUG_ASSERT(fixed == 1);
if (!forced_const && exec())
reset();
int2my_decimal(E_DEC_FATAL_ERROR, value, 0, decimal_value);
return decimal_value;
}
bool Item_exists_subselect::val_bool()
{
DBUG_ASSERT(fixed == 1);
if (!forced_const && exec())
{
reset();
return 0;
}
return value != 0;
}
double Item_in_subselect::val_real()
{
/*
As far as Item_in_subselect called only from Item_in_optimizer this
method should not be used
*/
DBUG_ASSERT(fixed == 1);
if (forced_const)
return value;
DBUG_ASSERT((engine->uncacheable() & ~UNCACHEABLE_EXPLAIN) ||
! engine->is_executed());
null_value= was_null= FALSE;
if (exec())
{
reset();
return 0;
}
if (was_null && !value)
null_value= TRUE;
return (double) value;
}
longlong Item_in_subselect::val_int()
{
/*
As far as Item_in_subselect called only from Item_in_optimizer this
method should not be used
*/
DBUG_ASSERT(0);
DBUG_ASSERT(fixed == 1);
if (forced_const)
return value;
DBUG_ASSERT((engine->uncacheable() & ~UNCACHEABLE_EXPLAIN) ||
! engine->is_executed());
null_value= was_null= FALSE;
if (exec())
{
reset();
return 0;
}
if (was_null && !value)
null_value= TRUE;
return value;
}
String *Item_in_subselect::val_str(String *str)
{
/*
As far as Item_in_subselect called only from Item_in_optimizer this
method should not be used
*/
DBUG_ASSERT(0);
DBUG_ASSERT(fixed == 1);
if (forced_const)
goto value_is_ready;
DBUG_ASSERT((engine->uncacheable() & ~UNCACHEABLE_EXPLAIN) ||
! engine->is_executed());
null_value= was_null= FALSE;
if (exec())
{
reset();
return 0;
}
if (was_null && !value)
{
null_value= TRUE;
return 0;
}
value_is_ready:
str->set((ulonglong)value, &my_charset_bin);
return str;
}
bool Item_in_subselect::val_bool()
{
DBUG_ASSERT(fixed == 1);
if (forced_const)
return value;
DBUG_ASSERT((engine->uncacheable() & ~UNCACHEABLE_EXPLAIN) ||
! engine->is_executed() || with_recursive_reference);
null_value= was_null= FALSE;
if (exec())
{
reset();
return 0;
}
if (was_null && !value)
null_value= TRUE;
return value;
}
my_decimal *Item_in_subselect::val_decimal(my_decimal *decimal_value)
{
/*
As far as Item_in_subselect called only from Item_in_optimizer this
method should not be used
*/
DBUG_ASSERT(0);
if (forced_const)
goto value_is_ready;
DBUG_ASSERT((engine->uncacheable() & ~UNCACHEABLE_EXPLAIN) ||
! engine->is_executed());
null_value= was_null= FALSE;
DBUG_ASSERT(fixed == 1);
if (exec())
{
reset();
return 0;
}
if (was_null && !value)
null_value= TRUE;
value_is_ready:
int2my_decimal(E_DEC_FATAL_ERROR, value, 0, decimal_value);
return decimal_value;
}
/**
Prepare a single-column IN/ALL/ANY subselect for rewriting.
@param join Join object of the subquery (i.e. 'child' join).
@details
Prepare a single-column subquery to be rewritten. Given the subquery.
If the subquery has no tables it will be turned to an expression between
left part and SELECT list.
In other cases the subquery will be wrapped with Item_in_optimizer which
allow later to turn it to EXISTS or MAX/MIN.
@retval false The subquery was transformed
@retval true Error
*/
bool
Item_in_subselect::single_value_transformer(JOIN *join)
{
SELECT_LEX *select_lex= join->select_lex;
DBUG_ENTER("Item_in_subselect::single_value_transformer");
DBUG_ASSERT(thd == join->thd);
/*
Check that the right part of the subselect contains no more than one
column. E.g. in SELECT 1 IN (SELECT * ..) the right part is (SELECT * ...)
*/
// psergey: duplicated_subselect_card_check
if (select_lex->item_list.elements > 1)
{
my_error(ER_OPERAND_COLUMNS, MYF(0), 1);
DBUG_RETURN(true);
}
Item* join_having= join->having ? join->having : join->tmp_having;
if (!(join_having || select_lex->with_sum_func ||
select_lex->group_list.elements) &&
select_lex->table_list.elements == 0 && !join->conds &&
!select_lex->master_unit()->is_unit_op())
{
Item *where_item= (Item*) select_lex->item_list.head();
/*
it is single select without tables => possible optimization
remove the dependence mark since the item is moved to upper
select and is not outer anymore.
*/
where_item->walk(&Item::remove_dependence_processor, 0,
select_lex->outer_select());
/*
fix_field of substitution item will be done in time of
substituting.
Note that real_item() should be used instead of
original left expression because left_expr can be
runtime created Ref item which is deleted at the end
of the statement. Thus one of 'substitution' arguments
can be broken in case of PS.
*/
substitution= func->create(thd, left_expr, where_item);
have_to_be_excluded= 1;
if (thd->lex->describe)
{
char warn_buff[MYSQL_ERRMSG_SIZE];
sprintf(warn_buff, ER_THD(thd, ER_SELECT_REDUCED),
select_lex->select_number);
push_warning(thd, Sql_condition::WARN_LEVEL_NOTE,
ER_SELECT_REDUCED, warn_buff);
}
DBUG_RETURN(false);
}
/*
Wrap the current IN predicate in an Item_in_optimizer. The actual
substitution in the Item tree takes place in Item_subselect::fix_fields.
*/
if (!substitution)
{
/* We're invoked for the 1st (or the only) SELECT in the subquery UNION */
substitution= optimizer;
SELECT_LEX *current= thd->lex->current_select;
thd->lex->current_select= current->return_after_parsing();
if (!optimizer || optimizer->fix_left(thd))
{
thd->lex->current_select= current;
DBUG_RETURN(true);
}
thd->lex->current_select= current;
/* We will refer to upper level cache array => we have to save it for SP */
optimizer->keep_top_level_cache();
/*
As far as Item_in_optimizer does not substitute itself on fix_fields
we can use same item for all selects.
*/
expr= new (thd->mem_root) Item_direct_ref(thd, &select_lex->context,
(Item**)optimizer->get_cache(),
"<no matter>",
&in_left_expr_name);
}
DBUG_RETURN(false);
}
/**
Apply transformation max/min transwormation to ALL/ANY subquery if it is
possible.
@param join Join object of the subquery (i.e. 'child' join).
@details
If this is an ALL/ANY single-value subselect, try to rewrite it with
a MIN/MAX subselect. We can do that if a possible NULL result of the
subselect can be ignored.
E.g. SELECT * FROM t1 WHERE b > ANY (SELECT a FROM t2) can be rewritten
with SELECT * FROM t1 WHERE b > (SELECT MAX(a) FROM t2).
We can't check that this optimization is safe if it's not a top-level
item of the WHERE clause (e.g. because the WHERE clause can contain IS
NULL/IS NOT NULL functions). If so, we rewrite ALL/ANY with NOT EXISTS
later in this method.
@retval false The subquery was transformed
@retval true Error
*/
bool Item_allany_subselect::transform_into_max_min(JOIN *join)
{
DBUG_ENTER("Item_allany_subselect::transform_into_max_min");
if (!test_strategy(SUBS_MAXMIN_INJECTED | SUBS_MAXMIN_ENGINE))
DBUG_RETURN(false);
Item **place= optimizer->arguments() + 1;
SELECT_LEX *select_lex= join->select_lex;
Item *subs;
DBUG_ASSERT(thd == join->thd);
/*
*/
DBUG_ASSERT(!substitution);
/*
Check if optimization with aggregate min/max possible
1 There is no aggregate in the subquery
2 It is not UNION
3 There is tables
4 It is not ALL subquery with possible NULLs in the SELECT list
*/
if (!select_lex->group_list.elements && /*1*/
!select_lex->having && /*1*/
!select_lex->with_sum_func && /*1*/
!(select_lex->next_select()) && /*2*/
select_lex->table_list.elements && /*3*/
(!select_lex->ref_pointer_array[0]->maybe_null || /*4*/
substype() != Item_subselect::ALL_SUBS)) /*4*/
{
Item_sum_min_max *item;
nesting_map save_allow_sum_func;
if (func->l_op())
{
/*
(ALL && (> || =>)) || (ANY && (< || =<))
for ALL condition is inverted
*/
item= new (thd->mem_root) Item_sum_max(thd,
select_lex->ref_pointer_array[0]);
}
else
{
/*
(ALL && (< || =<)) || (ANY && (> || =>))
for ALL condition is inverted
*/
item= new (thd->mem_root) Item_sum_min(thd,
select_lex->ref_pointer_array[0]);
}
if (upper_item)
upper_item->set_sum_test(item);
thd->change_item_tree(&select_lex->ref_pointer_array[0], item);
{
List_iterator<Item> it(select_lex->item_list);
it++;
thd->change_item_tree(it.ref(), item);
}
DBUG_EXECUTE("where",
print_where(item, "rewrite with MIN/MAX", QT_ORDINARY););
save_allow_sum_func= thd->lex->allow_sum_func;
thd->lex->allow_sum_func.set_bit(thd->lex->current_select->nest_level);
/*
Item_sum_(max|min) can't substitute other item => we can use 0 as
reference, also Item_sum_(max|min) can't be fixed after creation, so
we do not check item->fixed
*/
if (item->fix_fields(thd, 0))
DBUG_RETURN(true);
thd->lex->allow_sum_func= save_allow_sum_func;
/* we added aggregate function => we have to change statistic */
count_field_types(select_lex, &join->tmp_table_param, join->all_fields,
0);
if (join->prepare_stage2())
DBUG_RETURN(true);
subs= new (thd->mem_root) Item_singlerow_subselect(thd, select_lex);
/*
Remove other strategies if any (we already changed the query and
can't apply other strategy).
*/
set_strategy(SUBS_MAXMIN_INJECTED);
}
else
{
Item_maxmin_subselect *item;
subs= item= new (thd->mem_root) Item_maxmin_subselect(thd, this, select_lex, func->l_op());
if (upper_item)
upper_item->set_sub_test(item);
/*
Remove other strategies if any (we already changed the query and
can't apply other strategy).
*/
set_strategy(SUBS_MAXMIN_ENGINE);
}
/*
The swap is needed for expressions of type 'f1 < ALL ( SELECT ....)'
where we want to evaluate the sub query even if f1 would be null.
*/
subs= func->create_swap(thd, expr, subs);
thd->change_item_tree(place, subs);
if (subs->fix_fields(thd, &subs))
DBUG_RETURN(true);
DBUG_ASSERT(subs == (*place)); // There was no substitutions
select_lex->master_unit()->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
select_lex->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
DBUG_RETURN(false);
}
bool Item_in_subselect::fix_having(Item *having, SELECT_LEX *select_lex)
{
bool fix_res= 0;
DBUG_ASSERT(thd);
if (!having->fixed)
{
select_lex->having_fix_field= 1;
fix_res= having->fix_fields(thd, 0);
select_lex->having_fix_field= 0;
}
return fix_res;
}
bool Item_allany_subselect::is_maxmin_applicable(JOIN *join)
{
/*
Check if max/min optimization applicable: It is top item of
WHERE condition.
*/
return (abort_on_null || (upper_item && upper_item->is_top_level_item())) &&
!(join->select_lex->master_unit()->uncacheable & ~UNCACHEABLE_EXPLAIN) && !func->eqne_op();
}
/**
Create the predicates needed to transform a single-column IN/ALL/ANY
subselect into a correlated EXISTS via predicate injection.
@param join[in] Join object of the subquery (i.e. 'child' join).
@param where_item[out] the in-to-exists addition to the where clause
@param having_item[out] the in-to-exists addition to the having clause
@details
The correlated predicates are created as follows:
- If the subquery has aggregates, GROUP BY, or HAVING, convert to
SELECT ie FROM ... HAVING subq_having AND
trigcond(oe $cmp$ ref_or_null_helper<ie>)
the addition is wrapped into trigger only when we want to distinguish
between NULL and FALSE results.
- Otherwise (no aggregates/GROUP BY/HAVING) convert it to one of the
following:
= If we don't need to distinguish between NULL and FALSE subquery:
SELECT ie FROM ... WHERE subq_where AND (oe $cmp$ ie)
= If we need to distinguish between those:
SELECT ie FROM ...
WHERE subq_where AND trigcond((oe $cmp$ ie) OR (ie IS NULL))
HAVING trigcond(<is_not_null_test>(ie))
@retval false If the new conditions were created successfully
@retval true Error
*/
bool
Item_in_subselect::create_single_in_to_exists_cond(JOIN *join,
Item **where_item,
Item **having_item)
{
SELECT_LEX *select_lex= join->select_lex;
DBUG_ASSERT(thd == join->thd);
/*
The non-transformed HAVING clause of 'join' may be stored in two ways
during JOIN::optimize: this->tmp_having= this->having; this->having= 0;
*/
Item* join_having= join->having ? join->having : join->tmp_having;
DBUG_ENTER("Item_in_subselect::create_single_in_to_exists_cond");
*where_item= NULL;
*having_item= NULL;
if (join_having || select_lex->with_sum_func ||
select_lex->group_list.elements)
{
const char *tmp= this->full_name();
LEX_CSTRING field_name= {tmp, safe_strlen(tmp)};
Item *item= func->create(thd, expr,
new (thd->mem_root) Item_ref_null_helper(
thd,
&select_lex->context,
this,
&select_lex->
ref_pointer_array[0],
(char *)"<ref>",
&field_name));
if (!abort_on_null && left_expr->maybe_null)
{
/*
We can encounter "NULL IN (SELECT ...)". Wrap the added condition
within a trig_cond.
*/
disable_cond_guard_for_const_null_left_expr(0);
item= new (thd->mem_root) Item_func_trig_cond(thd, item, get_cond_guard(0));
}
if (!join_having)
item->name= in_having_cond;
if (fix_having(item, select_lex))
DBUG_RETURN(true);
*having_item= item;
}
else
{
/*
No need to use real_item for the item, as the ref items that are possible
in the subquery either belong to views or to the parent select.
For such case we need to refer to the reference and not to the original
item.
*/
Item *item= (Item*) select_lex->item_list.head();
if (select_lex->table_list.elements ||
!(select_lex->master_unit()->is_unit_op()))
{
Item *having= item;
Item *orig_item= item;
item= func->create(thd, expr, item);
if (!abort_on_null && orig_item->maybe_null)
{
having= new (thd->mem_root) Item_is_not_null_test(thd, this, having);
if (left_expr->maybe_null)
{
disable_cond_guard_for_const_null_left_expr(0);
if (!(having= new (thd->mem_root) Item_func_trig_cond(thd, having,
get_cond_guard(0))))
DBUG_RETURN(true);
}
having->name= in_having_cond;
if (fix_having(having, select_lex))
DBUG_RETURN(true);
*having_item= having;
item= new (thd->mem_root) Item_cond_or(thd, item,
new (thd->mem_root) Item_func_isnull(thd, orig_item));
}
/*
If we may encounter NULL IN (SELECT ...) and care whether subquery
result is NULL or FALSE, wrap condition in a trig_cond.
*/
if (!abort_on_null && left_expr->maybe_null)
{
disable_cond_guard_for_const_null_left_expr(0);
if (!(item= new (thd->mem_root) Item_func_trig_cond(thd, item,
get_cond_guard(0))))
DBUG_RETURN(true);
}
/*
TODO: figure out why the following is done here in
single_value_transformer but there is no corresponding action in
row_value_transformer?
*/
item->name= in_additional_cond;
if (item->fix_fields_if_needed(thd, 0))
DBUG_RETURN(true);
*where_item= item;
}
else
{
DBUG_ASSERT(select_lex->master_unit()->is_unit_op());
LEX_CSTRING field_name= {STRING_WITH_LEN("<result>") };
Item *new_having=
func->create(thd, expr,
new (thd->mem_root) Item_ref_null_helper(thd,
&select_lex->context,
this,
&select_lex->ref_pointer_array[0],
(char *)"<no matter>",
&field_name));
if (!abort_on_null && left_expr->maybe_null)
{
disable_cond_guard_for_const_null_left_expr(0);
if (!(new_having= new (thd->mem_root) Item_func_trig_cond(thd, new_having,
get_cond_guard(0))))
DBUG_RETURN(true);
}
new_having->name= in_having_cond;
if (fix_having(new_having, select_lex))
DBUG_RETURN(true);
*having_item= new_having;
}
}
DBUG_RETURN(false);
}
/**
Wrap a multi-column IN/ALL/ANY subselect into an Item_in_optimizer.
@param join Join object of the subquery (i.e. 'child' join).
@details
The subquery predicate is wrapped into an Item_in_optimizer. Later the query
optimization phase chooses whether the subquery under the Item_in_optimizer
will be further transformed into an equivalent correlated EXISTS by injecting
additional predicates, or will be executed via subquery materialization in its
unmodified form.
@retval false The subquery was transformed
@retval true Error
*/
bool
Item_in_subselect::row_value_transformer(JOIN *join)
{
SELECT_LEX *select_lex= join->select_lex;
uint cols_num= left_expr->cols();
DBUG_ENTER("Item_in_subselect::row_value_transformer");
DBUG_ASSERT(thd == join->thd);
// psergey: duplicated_subselect_card_check
if (select_lex->item_list.elements != cols_num)
{
my_error(ER_OPERAND_COLUMNS, MYF(0), cols_num);
DBUG_RETURN(true);
}
/*
Wrap the current IN predicate in an Item_in_optimizer. The actual
substitution in the Item tree takes place in Item_subselect::fix_fields.
*/
if (!substitution)
{
//first call for this unit
SELECT_LEX_UNIT *master_unit= select_lex->master_unit();
substitution= optimizer;
SELECT_LEX *current= thd->lex->current_select;
thd->lex->current_select= current->return_after_parsing();
if (!optimizer || optimizer->fix_left(thd))
{
thd->lex->current_select= current;
DBUG_RETURN(true);
}
// we will refer to upper level cache array => we have to save it in PS
optimizer->keep_top_level_cache();
thd->lex->current_select= current;
/*
The uncacheable property controls a number of actions, e.g. whether to
save/restore (via init_save_join_tab/restore_tmp) the original JOIN for
plans with a temp table where the original JOIN was overridden by
make_simple_join. The UNCACHEABLE_EXPLAIN is ignored by EXPLAIN, thus
non-correlated subqueries will not appear as such to EXPLAIN.
*/
master_unit->uncacheable|= UNCACHEABLE_EXPLAIN;
select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
}
DBUG_RETURN(false);
}
/**
Create the predicates needed to transform a multi-column IN/ALL/ANY
subselect into a correlated EXISTS via predicate injection.
@details
The correlated predicates are created as follows:
- If the subquery has aggregates, GROUP BY, or HAVING, convert to
(l1, l2, l3) IN (SELECT v1, v2, v3 ... HAVING having)
=>
EXISTS (SELECT ... HAVING having and
(l1 = v1 or is null v1) and
(l2 = v2 or is null v2) and
(l3 = v3 or is null v3) and
is_not_null_test(v1) and
is_not_null_test(v2) and
is_not_null_test(v3))
where is_not_null_test used to register nulls in case if we have
not found matching to return correct NULL value.
- Otherwise (no aggregates/GROUP BY/HAVING) convert the subquery as follows:
(l1, l2, l3) IN (SELECT v1, v2, v3 ... WHERE where)
=>
EXISTS (SELECT ... WHERE where and
(l1 = v1 or is null v1) and
(l2 = v2 or is null v2) and
(l3 = v3 or is null v3)
HAVING is_not_null_test(v1) and
is_not_null_test(v2) and
is_not_null_test(v3))
where is_not_null_test registers NULLs values but reject rows.
in case when we do not need correct NULL, we have simpler construction:
EXISTS (SELECT ... WHERE where and
(l1 = v1) and
(l2 = v2) and
(l3 = v3)
@param join[in] Join object of the subquery (i.e. 'child' join).
@param where_item[out] the in-to-exists addition to the where clause
@param having_item[out] the in-to-exists addition to the having clause
@retval false If the new conditions were created successfully
@retval true Error
*/
bool
Item_in_subselect::create_row_in_to_exists_cond(JOIN * join,
Item **where_item,
Item **having_item)
{
SELECT_LEX *select_lex= join->select_lex;
uint cols_num= left_expr->cols();
/*
The non-transformed HAVING clause of 'join' may be stored in two ways
during JOIN::optimize: this->tmp_having= this->having; this->having= 0;
*/
Item* join_having= join->having ? join->having : join->tmp_having;
bool is_having_used= (join_having || select_lex->with_sum_func ||
select_lex->group_list.first ||
!select_lex->table_list.elements);
LEX_CSTRING list_ref= { STRING_WITH_LEN("<list ref>")};
DBUG_ENTER("Item_in_subselect::create_row_in_to_exists_cond");
DBUG_ASSERT(thd == join->thd);
*where_item= NULL;
*having_item= NULL;
if (is_having_used)
{
/* TODO: say here explicitly if the order of AND parts matters or not. */
Item *item_having_part2= 0;
for (uint i= 0; i < cols_num; i++)
{
DBUG_ASSERT((left_expr->fixed &&
select_lex->ref_pointer_array[i]->fixed) ||
(select_lex->ref_pointer_array[i]->type() == REF_ITEM &&
((Item_ref*)(select_lex->ref_pointer_array[i]))->ref_type() ==
Item_ref::OUTER_REF));
if (select_lex->ref_pointer_array[i]->
check_cols(left_expr->element_index(i)->cols()))
DBUG_RETURN(true);
Item *item_eq=
new (thd->mem_root)
Item_func_eq(thd, new (thd->mem_root)
Item_direct_ref(thd, &select_lex->context,
(*optimizer->get_cache())->
addr(i),
(char *)"<no matter>",
&in_left_expr_name),
new (thd->mem_root)
Item_ref(thd, &select_lex->context,
&select_lex->ref_pointer_array[i],
(char *)"<no matter>",
&list_ref));
Item *item_isnull=
new (thd->mem_root)
Item_func_isnull(thd,
new (thd->mem_root)
Item_ref(thd, &select_lex->context,
&select_lex->ref_pointer_array[i],
(char *)"<no matter>",
&list_ref));
Item *col_item= new (thd->mem_root)
Item_cond_or(thd, item_eq, item_isnull);
if (!abort_on_null && left_expr->element_index(i)->maybe_null &&
get_cond_guard(i))
{
disable_cond_guard_for_const_null_left_expr(i);
if (!(col_item= new (thd->mem_root)
Item_func_trig_cond(thd, col_item, get_cond_guard(i))))
DBUG_RETURN(true);
}
*having_item= and_items(thd, *having_item, col_item);
Item *item_nnull_test=
new (thd->mem_root)
Item_is_not_null_test(thd, this,
new (thd->mem_root)
Item_ref(thd, &select_lex->context,
&select_lex->
ref_pointer_array[i],
(char *)"<no matter>",
&list_ref));
if (!abort_on_null && left_expr->element_index(i)->maybe_null &&
get_cond_guard(i) )
{
disable_cond_guard_for_const_null_left_expr(i);
if (!(item_nnull_test=
new (thd->mem_root)
Item_func_trig_cond(thd, item_nnull_test, get_cond_guard(i))))
DBUG_RETURN(true);
}
item_having_part2= and_items(thd, item_having_part2, item_nnull_test);
item_having_part2->top_level_item();
}
*having_item= and_items(thd, *having_item, item_having_part2);
}
else
{
for (uint i= 0; i < cols_num; i++)
{
Item *item, *item_isnull;
DBUG_ASSERT((left_expr->fixed &&
select_lex->ref_pointer_array[i]->fixed) ||
(select_lex->ref_pointer_array[i]->type() == REF_ITEM &&
((Item_ref*)(select_lex->ref_pointer_array[i]))->ref_type() ==
Item_ref::OUTER_REF));
if (select_lex->ref_pointer_array[i]->
check_cols(left_expr->element_index(i)->cols()))
DBUG_RETURN(true);
item= new (thd->mem_root)
Item_func_eq(thd,
new (thd->mem_root)
Item_direct_ref(thd, &select_lex->context,
(*optimizer->get_cache())->
addr(i),
(char *)"<no matter>",
&in_left_expr_name),
new (thd->mem_root)
Item_direct_ref(thd, &select_lex->context,
&select_lex->
ref_pointer_array[i],
(char *)"<no matter>",
&list_ref));
if (!abort_on_null && select_lex->ref_pointer_array[i]->maybe_null)
{
Item *having_col_item=
new (thd->mem_root)
Item_is_not_null_test(thd, this,
new (thd->mem_root)
Item_ref(thd, &select_lex->context,
&select_lex->ref_pointer_array[i],
(char *)"<no matter>",
&list_ref));
item_isnull= new (thd->mem_root)
Item_func_isnull(thd,
new (thd->mem_root)
Item_direct_ref(thd, &select_lex->context,
&select_lex->
ref_pointer_array[i],
(char *)"<no matter>",
&list_ref));
item= new (thd->mem_root) Item_cond_or(thd, item, item_isnull);
if (left_expr->element_index(i)->maybe_null && get_cond_guard(i))
{
disable_cond_guard_for_const_null_left_expr(i);
if (!(item= new (thd->mem_root)
Item_func_trig_cond(thd, item, get_cond_guard(i))))
DBUG_RETURN(true);
if (!(having_col_item= new (thd->mem_root)
Item_func_trig_cond(thd, having_col_item, get_cond_guard(i))))
DBUG_RETURN(true);
}
*having_item= and_items(thd, *having_item, having_col_item);
}
if (!abort_on_null && left_expr->element_index(i)->maybe_null &&
get_cond_guard(i))
{
if (!(item= new (thd->mem_root)
Item_func_trig_cond(thd, item, get_cond_guard(i))))
DBUG_RETURN(true);
}
*where_item= and_items(thd, *where_item, item);
}
}
if (*where_item)
{
if ((*where_item)->fix_fields_if_needed(thd, 0))
DBUG_RETURN(true);
(*where_item)->top_level_item();
}
if (*having_item)
{
if (!join_having)
(*having_item)->name= in_having_cond;
if (fix_having(*having_item, select_lex))
DBUG_RETURN(true);
(*having_item)->top_level_item();
}
DBUG_RETURN(false);
}
bool
Item_in_subselect::select_transformer(JOIN *join)
{
return select_in_like_transformer(join);
}
bool
Item_exists_subselect::select_transformer(JOIN *join)
{
return select_prepare_to_be_in();
}
/**
Create the predicates needed to transform an IN/ALL/ANY subselect into a
correlated EXISTS via predicate injection.
@param join_arg Join object of the subquery.
@retval FALSE ok
@retval TRUE error
*/
bool Item_in_subselect::create_in_to_exists_cond(JOIN *join_arg)
{
bool res;
DBUG_ASSERT(engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE ||
engine->engine_type() == subselect_engine::UNION_ENGINE);
/*
TODO: the call to init_cond_guards allocates and initializes an
array of booleans that may not be used later because we may choose
materialization.
The two calls below to create_XYZ_cond depend on this boolean array.
If the dependency is removed, the call can be moved to a later phase.
*/
init_cond_guards();
if (left_expr->cols() == 1)
res= create_single_in_to_exists_cond(join_arg,
&(join_arg->in_to_exists_where),
&(join_arg->in_to_exists_having));
else
res= create_row_in_to_exists_cond(join_arg,
&(join_arg->in_to_exists_where),
&(join_arg->in_to_exists_having));
/*
The IN=>EXISTS transformation makes non-correlated subqueries correlated.
*/
if (!left_expr->const_item() || left_expr->is_expensive())
{
join_arg->select_lex->uncacheable|= UNCACHEABLE_DEPENDENT_INJECTED;
join_arg->select_lex->master_unit()->uncacheable|=
UNCACHEABLE_DEPENDENT_INJECTED;
}
/*
The uncacheable property controls a number of actions, e.g. whether to
save/restore (via init_save_join_tab/restore_tmp) the original JOIN for
plans with a temp table where the original JOIN was overridden by
make_simple_join. The UNCACHEABLE_EXPLAIN is ignored by EXPLAIN, thus
non-correlated subqueries will not appear as such to EXPLAIN.
*/
join_arg->select_lex->master_unit()->uncacheable|= UNCACHEABLE_EXPLAIN;
join_arg->select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
return (res);
}
/**
Transform an IN/ALL/ANY subselect into a correlated EXISTS via injecting
correlated in-to-exists predicates.
@param join_arg Join object of the subquery.
@retval FALSE ok
@retval TRUE error
*/
bool Item_in_subselect::inject_in_to_exists_cond(JOIN *join_arg)
{
SELECT_LEX *select_lex= join_arg->select_lex;
Item *where_item= join_arg->in_to_exists_where;
Item *having_item= join_arg->in_to_exists_having;
DBUG_ENTER("Item_in_subselect::inject_in_to_exists_cond");
DBUG_ASSERT(thd == join_arg->thd);
if (select_lex->min_max_opt_list.elements)
{
/*
MIN/MAX optimizations have been applied to Item_sum objects
of the subquery this subquery predicate in opt_sum_query().
Injection of new condition invalidates this optimizations.
Thus those optimizations must be rolled back.
*/
List_iterator_fast<Item_sum> it(select_lex->min_max_opt_list);
Item_sum *item;
while ((item= it++))
{
item->clear();
item->reset_forced_const();
}
if (where_item)
where_item->update_used_tables();
if (having_item)
having_item->update_used_tables();
}
if (where_item)
{
List<Item> *and_args= NULL;
/*
If the top-level Item of the WHERE clause is an AND, detach the multiple
equality list that was attached to the end of the AND argument list by
build_equal_items_for_cond(). The multiple equalities must be detached
because fix_fields merges lower level AND arguments into the upper AND.
As a result, the arguments from lower-level ANDs are concatenated after
the multiple equalities. When the multiple equality list is treated as
such, it turns out that it contains non-Item_equal object which is wrong.
*/
if (join_arg->conds && join_arg->conds->type() == Item::COND_ITEM &&
((Item_cond*) join_arg->conds)->functype() == Item_func::COND_AND_FUNC)
{
and_args= ((Item_cond*) join_arg->conds)->argument_list();
if (join_arg->cond_equal)
and_args->disjoin((List<Item> *) &join_arg->cond_equal->current_level);
}
where_item= and_items(thd, join_arg->conds, where_item);
/* This is the fix_fields() call mentioned in the comment above */
if (where_item->fix_fields_if_needed(thd, 0))
DBUG_RETURN(true);
// TIMOUR TODO: call optimize_cond() for the new where clause
thd->change_item_tree(&select_lex->where, where_item);
select_lex->where->top_level_item();
join_arg->conds= select_lex->where;
/* Attach back the list of multiple equalities to the new top-level AND. */
if (and_args && join_arg->cond_equal)
{
/*
The fix_fields() call above may have changed the argument list, so
fetch it again:
*/
and_args= ((Item_cond*) join_arg->conds)->argument_list();
((Item_cond_and *) (join_arg->conds))->m_cond_equal=
*join_arg->cond_equal;
and_args->append((List<Item> *)&join_arg->cond_equal->current_level);
}
}
if (having_item)
{
Item* join_having= join_arg->having ? join_arg->having:join_arg->tmp_having;
having_item= and_items(thd, join_having, having_item);
if (fix_having(having_item, select_lex))
DBUG_RETURN(true);
// TIMOUR TODO: call optimize_cond() for the new having clause
thd->change_item_tree(&select_lex->having, having_item);
select_lex->having->top_level_item();
join_arg->having= select_lex->having;
}
join_arg->thd->change_item_tree(&unit->global_parameters()->select_limit,
new (thd->mem_root)
Item_int(thd, (int32) 1));
unit->select_limit_cnt= 1;
DBUG_RETURN(false);
}
/*
If this select can potentially be converted by EXISTS->IN conversion, wrap it
in an Item_in_optimizer object. Final decision whether to do the conversion
is done at a later phase.
*/
bool Item_exists_subselect::select_prepare_to_be_in()
{
bool trans_res= FALSE;
DBUG_ENTER("Item_exists_subselect::select_prepare_to_be_in");
if (!optimizer &&
thd->lex->sql_command == SQLCOM_SELECT &&
!unit->first_select()->is_part_of_union() &&
optimizer_flag(thd, OPTIMIZER_SWITCH_EXISTS_TO_IN) &&
(is_top_level_item() ||
(upper_not && upper_not->is_top_level_item())))
{
Query_arena *arena, backup;
bool result;
arena= thd->activate_stmt_arena_if_needed(&backup);
result= (!(optimizer= new (thd->mem_root) Item_in_optimizer(thd, new (thd->mem_root) Item_int(thd, 1), this)));
if (arena)
thd->restore_active_arena(arena, &backup);
if (result)
trans_res= TRUE;
else
substitution= optimizer;
}
DBUG_RETURN(trans_res);
}
/**
Check if 'func' is an equality in form "inner_table.column = outer_expr"
@param func Expression to check
@param allow_subselect If true, the outer_expr part can have a subquery
If false, it cannot.
@param local_field OUT Return "inner_table.column" here
@param outer_expr OUT Return outer_expr here
@return true - 'func' is an Equality.
*/
static bool check_equality_for_exist2in(Item_func *func,
bool allow_subselect,
Item_ident **local_field,
Item **outer_exp)
{
Item **args;
if (func->functype() != Item_func::EQ_FUNC)
return FALSE;
DBUG_ASSERT(func->argument_count() == 2);
args= func->arguments();
if (args[0]->real_type() == Item::FIELD_ITEM &&
args[0]->all_used_tables() != OUTER_REF_TABLE_BIT &&
args[1]->all_used_tables() == OUTER_REF_TABLE_BIT &&
(allow_subselect || !args[1]->with_subquery()))
{
/* It is Item_field or Item_direct_view_ref) */
DBUG_ASSERT(args[0]->type() == Item::FIELD_ITEM ||
args[0]->type() == Item::REF_ITEM);
*local_field= (Item_ident *)args[0];
*outer_exp= args[1];
return TRUE;
}
else if (args[1]->real_type() == Item::FIELD_ITEM &&
args[1]->all_used_tables() != OUTER_REF_TABLE_BIT &&
args[0]->all_used_tables() == OUTER_REF_TABLE_BIT &&
(allow_subselect || !args[0]->with_subquery()))
{
/* It is Item_field or Item_direct_view_ref) */
DBUG_ASSERT(args[1]->type() == Item::FIELD_ITEM ||
args[1]->type() == Item::REF_ITEM);
*local_field= (Item_ident *)args[1];
*outer_exp= args[0];
return TRUE;
}
return FALSE;
}
typedef struct st_eq_field_outer
{
Item **eq_ref;
Item_ident *local_field;
Item *outer_exp;
} EQ_FIELD_OUTER;
/**
Check if 'conds' is a set of AND-ed outer_expr=inner_table.col equalities
@detail
Check if 'conds' has form
outer1=inner_tbl1.col1 AND ... AND outer2=inner_tbl1.col2 AND remainder_cond
if there is just one outer_expr=inner_expr pair, then outer_expr can have a
subselect in it. If there are many such pairs, then none of outer_expr can
have a subselect in it. If we allow this, the query will fail with an error:
This version of MariaDB doesn't yet support 'SUBQUERY in ROW in left
expression of IN/ALL/ANY'
@param conds Condition to be checked
@parm result Array to collect EQ_FIELD_OUTER elements describing
inner-vs-outer equalities the function has found.
@return
false - some inner-vs-outer equalities were found
true - otherwise.
*/
static bool find_inner_outer_equalities(Item **conds,
Dynamic_array<EQ_FIELD_OUTER> &result)
{
bool found= FALSE;
EQ_FIELD_OUTER element;
if (is_cond_and(*conds))
{
List_iterator<Item> li(*((Item_cond*)*conds)->argument_list());
Item *item;
bool allow_subselect= true;
while ((item= li++))
{
if (item->type() == Item::FUNC_ITEM &&
check_equality_for_exist2in((Item_func *)item,
allow_subselect,
&element.local_field,
&element.outer_exp))
{
found= TRUE;
allow_subselect= false;
element.eq_ref= li.ref();
if (result.append(element))
goto alloc_err;
}
}
}
else if ((*conds)->type() == Item::FUNC_ITEM &&
check_equality_for_exist2in((Item_func *)*conds,
true,
&element.local_field,
&element.outer_exp))
{
found= TRUE;
element.eq_ref= conds;
if (result.append(element))
goto alloc_err;
}
return !found;
alloc_err:
return TRUE;
}
/**
Converts EXISTS subquery to IN subquery if it is possible and has sense
@param opt_arg Pointer on THD
@return TRUE in case of error and FALSE otherwise.
*/
bool Item_exists_subselect::exists2in_processor(void *opt_arg)
{
THD *thd= (THD *)opt_arg;
SELECT_LEX *first_select=unit->first_select(), *save_select;
JOIN *join= first_select->join;
Item **eq_ref= NULL;
Item_ident *local_field= NULL;
Item *outer_exp= NULL;
Item *left_exp= NULL; Item_in_subselect *in_subs;
Query_arena *arena= NULL, backup;
int res= FALSE;
List<Item> outer;
Dynamic_array<EQ_FIELD_OUTER> eqs(5, 5);
bool will_be_correlated;
DBUG_ENTER("Item_exists_subselect::exists2in_processor");
if (!optimizer ||
!optimizer_flag(thd, OPTIMIZER_SWITCH_EXISTS_TO_IN) ||
(!is_top_level_item() && (!upper_not ||
!upper_not->is_top_level_item())) ||
first_select->is_part_of_union() ||
first_select->group_list.elements ||
first_select->order_list.elements ||
join->having ||
first_select->with_sum_func ||
!first_select->leaf_tables.elements||
!join->conds ||
with_recursive_reference)
DBUG_RETURN(FALSE);
DBUG_ASSERT(first_select->order_list.elements == 0 &&
first_select->group_list.elements == 0 &&
first_select->having == NULL);
if (find_inner_outer_equalities(&join->conds, eqs))
DBUG_RETURN(FALSE);
DBUG_ASSERT(eqs.elements() != 0);
save_select= thd->lex->current_select;
thd->lex->current_select= first_select;
/* check that the subquery has only dependencies we are going pull out */
{
List<Item> unused;
Collect_deps_prm prm= {&unused, // parameters
unit->first_select()->nest_level_base, // nest_level_base
0, // count
unit->first_select()->nest_level, // nest_level
FALSE // collect
};
walk(&Item::collect_outer_ref_processor, TRUE, &prm);
DBUG_ASSERT(prm.count > 0);
DBUG_ASSERT(prm.count >= (uint)eqs.elements());
will_be_correlated= prm.count > (uint)eqs.elements();
if (upper_not && will_be_correlated)
goto out;
}
if ((uint)eqs.elements() > (first_select->item_list.elements +
first_select->select_n_reserved))
goto out;
/* It is simple query */
DBUG_ASSERT(first_select->join->all_fields.elements ==
first_select->item_list.elements);
arena= thd->activate_stmt_arena_if_needed(&backup);
while (first_select->item_list.elements > (uint)eqs.elements())
{
first_select->item_list.pop();
first_select->join->all_fields.elements--;
}
{
List_iterator<Item> it(first_select->item_list);
for (uint i= 0; i < (uint)eqs.elements(); i++)
{
Item *item= it++;
eq_ref= eqs.at(i).eq_ref;
local_field= eqs.at(i).local_field;
outer_exp= eqs.at(i).outer_exp;
/* Add the field to the SELECT_LIST */
if (item)
it.replace(local_field);
else
{
first_select->item_list.push_back(local_field, thd->mem_root);
first_select->join->all_fields.elements++;
}
first_select->ref_pointer_array[i]= (Item *)local_field;
/* remove the parts from condition */
if (!upper_not || !local_field->maybe_null)
*eq_ref= new (thd->mem_root) Item_int(thd, 1);
else
{
*eq_ref= new (thd->mem_root)
Item_func_isnotnull(thd,
new (thd->mem_root)
Item_field(thd,
((Item_field*)(local_field->
real_item()))->context,
((Item_field*)(local_field->
real_item()))->field));
if((*eq_ref)->fix_fields(thd, (Item **)eq_ref))
{
res= TRUE;
goto out;
}
}
outer_exp->fix_after_pullout(unit->outer_select(), &outer_exp, FALSE);
outer_exp->update_used_tables();
outer.push_back(outer_exp, thd->mem_root);
}
}
join->conds->update_used_tables();
/* make IN SUBQUERY and put outer_exp as left part */
if (eqs.elements() == 1)
left_exp= outer_exp;
else
{
if (!(left_exp= new (thd->mem_root) Item_row(thd, outer)))
{
res= TRUE;
goto out;
}
}
/* make EXISTS->IN permanet (see Item_subselect::init()) */
set_exists_transformed();
first_select->select_limit= NULL;
if (!(in_subs= new (thd->mem_root) Item_in_subselect(thd, left_exp,
first_select)))
{
res= TRUE;
goto out;
}
in_subs->set_exists_transformed();
optimizer->arguments()[0]= left_exp;
optimizer->arguments()[1]= in_subs;
in_subs->optimizer= optimizer;
DBUG_ASSERT(is_top_level_item() ||
(upper_not && upper_not->is_top_level_item()));
in_subs->top_level_item();
{
SELECT_LEX *current= thd->lex->current_select;
optimizer->reset_cache(); // renew cache, and we will not keep it
thd->lex->current_select= unit->outer_select();
DBUG_ASSERT(optimizer);
if (optimizer->fix_left(thd))
{
res= TRUE;
/*
We should not restore thd->lex->current_select because it will be
reset on exit from this procedure
*/
goto out;
}
/*
As far as Item_ref_in_optimizer do not substitute itself on fix_fields
we can use same item for all selects.
*/
in_subs->expr= new (thd->mem_root)
Item_direct_ref(thd, &first_select->context,
(Item**)optimizer->get_cache(),
(char *)"<no matter>",
&in_left_expr_name);
if (in_subs->fix_fields(thd, optimizer->arguments() + 1))
{
res= TRUE;
/*
We should not restore thd->lex->current_select because it will be
reset on exit from this procedure
*/
goto out;
}
{
/* Move dependence list */
List_iterator_fast<Ref_to_outside> it(upper_refs);
Ref_to_outside *upper;
while ((upper= it++))
{
uint i;
for (i= 0; i < (uint)eqs.elements(); i++)
if (eqs.at(i).outer_exp->
walk(&Item::find_item_processor, TRUE, upper->item))
break;
if (i == (uint)eqs.elements() &&
(in_subs->upper_refs.push_back(upper, thd->stmt_arena->mem_root)))
goto out;
}
}
in_subs->update_used_tables();
/*
The engine of the subquery is fixed so above fix_fields() is not
complete and should be fixed
*/
in_subs->upper_refs= upper_refs;
upper_refs.empty();
thd->lex->current_select= current;
}
DBUG_ASSERT(unit->item == in_subs);
DBUG_ASSERT(join == first_select->join);
/*
Fix dependency info
*/
in_subs->is_correlated= will_be_correlated;
if (!will_be_correlated)
{
first_select->uncacheable&= ~UNCACHEABLE_DEPENDENT_GENERATED;
unit->uncacheable&= ~UNCACHEABLE_DEPENDENT_GENERATED;
}
/*
set possible optimization strategies
*/
in_subs->emb_on_expr_nest= emb_on_expr_nest;
res= check_and_do_in_subquery_rewrites(join);
first_select->join->prepare_stage2();
first_select->fix_prepare_information(thd, &join->conds, &join->having);
if (upper_not)
{
Item *exp;
if (eqs.elements() == 1)
{
exp= (optimizer->arguments()[0]->maybe_null ?
(Item*) new (thd->mem_root)
Item_cond_and(thd,
new (thd->mem_root)
Item_func_isnotnull(thd,
new (thd->mem_root)
Item_direct_ref(thd,
&unit->outer_select()->context,
optimizer->arguments(),
(char *)"<no matter>",
&exists_outer_expr_name)),
optimizer) :
(Item *)optimizer);
}
else
{
List<Item> *and_list= new List<Item>;
if (!and_list)
{
res= TRUE;
goto out;
}
for (size_t i= 0; i < eqs.elements(); i++)
{
if (optimizer->arguments()[0]->maybe_null)
{
and_list->
push_front(new (thd->mem_root)
Item_func_isnotnull(thd,
new (thd->mem_root)
Item_direct_ref(thd,
&unit->outer_select()->context,
optimizer->arguments()[0]->addr((int)i),
(char *)"<no matter>",
&exists_outer_expr_name)),
thd->mem_root);
}
}
if (and_list->elements > 0)
{
and_list->push_front(optimizer, thd->mem_root);
exp= new (thd->mem_root) Item_cond_and(thd, *and_list);
}
else
exp= optimizer;
}
upper_not->arguments()[0]= exp;
if (exp->fix_fields_if_needed(thd, upper_not->arguments()))
{
res= TRUE;
goto out;
}
}
out:
thd->lex->current_select= save_select;
if (arena)
thd->restore_active_arena(arena, &backup);
DBUG_RETURN(res);
}
/**
Prepare IN/ALL/ANY/SOME subquery transformation and call the appropriate
transformation function.
@param join JOIN object of transforming subquery
@notes
To decide which transformation procedure (scalar or row) applicable here
we have to call fix_fields() for the left expression to be able to call
cols() method on it. Also this method makes arena management for
underlying transformation methods.
@retval false OK
@retval true Error
*/
bool
Item_in_subselect::select_in_like_transformer(JOIN *join)
{
Query_arena *arena= 0, backup;
SELECT_LEX *current= thd->lex->current_select;
const char *save_where= thd->where;
bool trans_res= true;
bool result;
DBUG_ENTER("Item_in_subselect::select_in_like_transformer");
DBUG_ASSERT(thd == join->thd);
/*
IN/SOME/ALL/ANY subqueries aren't support LIMIT clause. Without it
ORDER BY clause becomes meaningless thus we drop it here.
*/
for (SELECT_LEX *sl= current->master_unit()->first_select();
sl; sl= sl->next_select())
{
if (sl->join)
{
sl->join->order= 0;
sl->join->skip_sort_order= 1;
}
}
thd->where= "IN/ALL/ANY subquery";
/*
In some optimisation cases we will not need this Item_in_optimizer
object, but we can't know it here, but here we need address correct
reference on left expression.
note: we won't need Item_in_optimizer when handling degenerate cases
like "... IN (SELECT 1)"
*/
arena= thd->activate_stmt_arena_if_needed(&backup);
if (!optimizer)
{
optimizer= new (thd->mem_root) Item_in_optimizer(thd, left_expr_orig, this);
if ((result= !optimizer))
goto out;
}
thd->lex->current_select= current->return_after_parsing();
result= optimizer->fix_left(thd);
thd->lex->current_select= current;
if (changed)
{
trans_res= false;
goto out;
}
if (result)
goto out;
/*
Both transformers call fix_fields() only for Items created inside them,
and all that items do not make permanent changes in current item arena
which allow to us call them with changed arena (if we do not know nature
of Item, we have to call fix_fields() for it only with original arena to
avoid memory leak)
*/
if (left_expr->cols() == 1)
trans_res= single_value_transformer(join);
else
{
/* we do not support row operation for ALL/ANY/SOME */
if (func != &eq_creator)
{
if (arena)
thd->restore_active_arena(arena, &backup);
my_error(ER_OPERAND_COLUMNS, MYF(0), 1);
DBUG_RETURN(true);
}
trans_res= row_value_transformer(join);
}
out:
if (arena)
thd->restore_active_arena(arena, &backup);
thd->where= save_where;
DBUG_RETURN(trans_res);
}
void Item_in_subselect::print(String *str, enum_query_type query_type)
{
if (test_strategy(SUBS_IN_TO_EXISTS))
str->append(STRING_WITH_LEN("<exists>"));
else
{
left_expr->print_parenthesised(str, query_type, precedence());
str->append(STRING_WITH_LEN(" in "));
}
Item_subselect::print(str, query_type);
}
bool Item_exists_subselect::fix_fields(THD *thd, Item **ref)
{
DBUG_ENTER("Item_exists_subselect::fix_fields");
if (exists_transformed)
DBUG_RETURN( !( (*ref)= new (thd->mem_root) Item_int(thd, 1)));
DBUG_RETURN(Item_subselect::fix_fields(thd, ref));
}
bool Item_in_subselect::fix_fields(THD *thd_arg, Item **ref)
{
uint outer_cols_num;
List<Item> *inner_cols;
char const *save_where= thd_arg->where;
DBUG_ENTER("Item_in_subselect::fix_fields");
thd= thd_arg;
DBUG_ASSERT(unit->thd == thd);
if (test_strategy(SUBS_SEMI_JOIN))
DBUG_RETURN( !( (*ref)= new (thd->mem_root) Item_int(thd, 1)) );
thd->where= "IN/ALL/ANY subquery";
/*
Check if the outer and inner IN operands match in those cases when we
will not perform IN=>EXISTS transformation. Currently this is when we
use subquery materialization.
The condition below is true when this method was called recursively from
inside JOIN::prepare for the JOIN object created by the call chain
Item_subselect::fix_fields -> subselect_single_select_engine::prepare,
which creates a JOIN object for the subquery and calls JOIN::prepare for
the JOIN of the subquery.
Notice that in some cases, this doesn't happen, and the check_cols()
test for each Item happens later in
Item_in_subselect::row_value_in_to_exists_transformer.
The reason for this mess is that our JOIN::prepare phase works top-down
instead of bottom-up, so we first do name resoluton and semantic checks
for the outer selects, then for the inner.
*/
if (engine &&
engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE &&
((subselect_single_select_engine*)engine)->join)
{
outer_cols_num= left_expr->cols();
if (unit->is_unit_op())
inner_cols= &(unit->types);
else
inner_cols= &(unit->first_select()->item_list);
if (outer_cols_num != inner_cols->elements)
{
my_error(ER_OPERAND_COLUMNS, MYF(0), outer_cols_num);
goto err;
}
if (outer_cols_num > 1)
{
List_iterator<Item> inner_col_it(*inner_cols);
Item *inner_col;
for (uint i= 0; i < outer_cols_num; i++)
{
inner_col= inner_col_it++;
if (inner_col->check_cols(left_expr->element_index(i)->cols()))
goto err;
}
}
}
if (left_expr && left_expr->fix_fields_if_needed(thd_arg, &left_expr))
goto err;
else
if (Item_subselect::fix_fields(thd_arg, ref))
goto err;
fixed= TRUE;
thd->where= save_where;
DBUG_RETURN(FALSE);
err:
thd->where= save_where;
DBUG_RETURN(TRUE);
}
void Item_in_subselect::fix_after_pullout(st_select_lex *new_parent,
Item **ref, bool merge)
{
left_expr->fix_after_pullout(new_parent, &left_expr, merge);
Item_subselect::fix_after_pullout(new_parent, ref, merge);
used_tables_cache |= left_expr->used_tables();
}
void Item_in_subselect::update_used_tables()
{
Item_subselect::update_used_tables();
left_expr->update_used_tables();
//used_tables_cache |= left_expr->used_tables();
used_tables_cache= Item_subselect::used_tables() | left_expr->used_tables();
}
/**
Try to create and initialize an engine to compute a subselect via
materialization.
@details
The method creates a new engine for materialized execution, and initializes
the engine. The initialization may fail
- either because it wasn't possible to create the needed temporary table
and its index,
- or because of a memory allocation error,
@returns
@retval TRUE memory allocation error occurred
@retval FALSE an execution method was chosen successfully
*/
bool Item_in_subselect::setup_mat_engine()
{
subselect_hash_sj_engine *mat_engine= NULL;
subselect_single_select_engine *select_engine;
DBUG_ENTER("Item_in_subselect::setup_mat_engine");
DBUG_ASSERT(thd);
/*
The select_engine (that executes transformed IN=>EXISTS subselects) is
pre-created at parse time, and is stored in statement memory (preserved
across PS executions).
*/
DBUG_ASSERT(engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE);
select_engine= (subselect_single_select_engine*) engine;
/* Create/initialize execution objects. */
if (!(mat_engine= new subselect_hash_sj_engine(thd, this, select_engine)))
DBUG_RETURN(TRUE);
if (mat_engine->prepare(thd) ||
mat_engine->init(&select_engine->join->fields_list,
engine->get_identifier()))
DBUG_RETURN(TRUE);
engine= mat_engine;
DBUG_RETURN(FALSE);
}
/**
Initialize the cache of the left operand of the IN predicate.
@note This method has the same purpose as alloc_group_fields(),
but it takes a different kind of collection of items, and the
list we push to is dynamically allocated.
@retval TRUE if a memory allocation error occurred or the cache is
not applicable to the current query
@retval FALSE if success
*/
bool Item_in_subselect::init_left_expr_cache()
{
JOIN *outer_join;
DBUG_ASSERT(thd);
outer_join= unit->outer_select()->join;
/*
An IN predicate might be evaluated in a query for which all tables have
been optimzied away.
*/
if (!outer_join || !outer_join->table_count || !outer_join->tables_list)
return TRUE;
if (!(left_expr_cache= new List<Cached_item>))
return TRUE;
for (uint i= 0; i < left_expr->cols(); i++)
{
Cached_item *cur_item_cache= new_Cached_item(thd,
left_expr->element_index(i),
FALSE);
if (!cur_item_cache || left_expr_cache->push_front(cur_item_cache,
thd->mem_root))
return TRUE;
}
return FALSE;
}
bool Item_in_subselect::init_cond_guards()
{
DBUG_ASSERT(thd);
uint cols_num= left_expr->cols();
if (!abort_on_null && !pushed_cond_guards &&
(left_expr->maybe_null || cols_num > 1))
{
if (!(pushed_cond_guards= (bool*)thd->alloc(sizeof(bool) * cols_num)))
return TRUE;
for (uint i= 0; i < cols_num; i++)
pushed_cond_guards[i]= TRUE;
}
return FALSE;
}
bool
Item_allany_subselect::select_transformer(JOIN *join)
{
DBUG_ENTER("Item_allany_subselect::select_transformer");
DBUG_ASSERT((in_strategy & ~(SUBS_MAXMIN_INJECTED | SUBS_MAXMIN_ENGINE |
SUBS_IN_TO_EXISTS | SUBS_STRATEGY_CHOSEN)) == 0);
if (upper_item)
upper_item->show= 1;
DBUG_RETURN(select_in_like_transformer(join));
}
void Item_allany_subselect::print(String *str, enum_query_type query_type)
{
if (test_strategy(SUBS_IN_TO_EXISTS))
str->append(STRING_WITH_LEN("<exists>"));
else
{
left_expr->print(str, query_type);
str->append(' ');
str->append(func->symbol(all));
str->append(all ? " all " : " any ", 5);
}
Item_subselect::print(str, query_type);
}
void Item_allany_subselect::no_rows_in_result()
{
/*
Subquery predicates outside of the SELECT list must be evaluated in order
to possibly filter the special result row generated for implicit grouping
if the subquery is in the HAVING clause.
If the predicate is constant, we need its actual value in the only result
row for queries with implicit grouping.
*/
if (parsing_place != SELECT_LIST || const_item())
return;
value= 0;
null_value= 0;
was_null= 0;
make_const();
}
void subselect_engine::set_thd(THD *thd_arg)
{
thd= thd_arg;
if (result)
result->set_thd(thd_arg);
}
subselect_single_select_engine::
subselect_single_select_engine(st_select_lex *select,
select_result_interceptor *result_arg,
Item_subselect *item_arg)
:subselect_engine(item_arg, result_arg),
prepared(0), executed(0),
select_lex(select), join(0)
{
select_lex->master_unit()->item= item_arg;
}
int subselect_single_select_engine::get_identifier()
{
return select_lex->select_number;
}
void subselect_single_select_engine::force_reexecution()
{
executed= false;
}
void subselect_single_select_engine::cleanup()
{
DBUG_ENTER("subselect_single_select_engine::cleanup");
prepared= executed= 0;
join= 0;
result->cleanup();
select_lex->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
DBUG_VOID_RETURN;
}
void subselect_union_engine::cleanup()
{
DBUG_ENTER("subselect_union_engine::cleanup");
unit->reinit_exec_mechanism();
result->cleanup();
unit->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
sl->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
DBUG_VOID_RETURN;
}
bool subselect_union_engine::is_executed() const
{
return unit->executed;
}
void subselect_union_engine::force_reexecution()
{
unit->executed= false;
}
/*
Check if last execution of the subquery engine produced any rows
SYNOPSIS
subselect_union_engine::no_rows()
DESCRIPTION
Check if last execution of the subquery engine produced any rows. The
return value is undefined if last execution ended in an error.
RETURN
TRUE - Last subselect execution has produced no rows
FALSE - Otherwise
*/
bool subselect_union_engine::no_rows()
{
/* Check if we got any rows when reading UNION result from temp. table: */
if (unit->fake_select_lex)
{
JOIN *join= unit->fake_select_lex->join;
if (join)
return MY_TEST(!join->send_records);
return false;
}
return MY_TEST(!(((select_union_direct *)(unit->get_union_result()))
->send_records));
}
void subselect_uniquesubquery_engine::cleanup()
{
DBUG_ENTER("subselect_uniquesubquery_engine::cleanup");
/*
Note for mergers: we don't have to, and actually must not de-initialize
tab->table->file here.
- We don't have to, because free_tmp_table() will call ha_index_or_rnd_end
- We must not do it, because tab->table may be a derived table which
has been already dropped by close_thread_tables(), while we here are
called from cleanup_items()
*/
DBUG_VOID_RETURN;
}
subselect_union_engine::subselect_union_engine(st_select_lex_unit *u,
select_result_interceptor *result_arg,
Item_subselect *item_arg)
:subselect_engine(item_arg, result_arg)
{
unit= u;
unit->item= item_arg;
}
/**
Create and prepare the JOIN object that represents the query execution
plan for the subquery.
@details
This method is called from Item_subselect::fix_fields. For prepared
statements it is called both during the PREPARE and EXECUTE phases in the
following ways:
- During PREPARE the optimizer needs some properties
(join->fields_list.elements) of the JOIN to proceed with preparation of
the remaining query (namely to complete ::fix_fields for the subselect
related classes. In the end of PREPARE the JOIN is deleted.
- When we EXECUTE the query, Item_subselect::fix_fields is called again, and
the JOIN object is re-created again, prepared and executed. In the end of
execution it is deleted.
In all cases the JOIN is created in runtime memory (not in the permanent
memory root).
@todo
Re-check what properties of 'join' are needed during prepare, and see if
we can avoid creating a JOIN during JOIN::prepare of the outer join.
@retval 0 if success
@retval 1 if error
*/
int subselect_single_select_engine::prepare(THD *thd)
{
if (prepared)
return 0;
set_thd(thd);
if (select_lex->join)
{
select_lex->cleanup();
}
join= new JOIN(thd, select_lex->item_list,
select_lex->options | SELECT_NO_UNLOCK, result);
if (!join || !result)
return 1; /* Fatal error is set already. */
prepared= 1;
SELECT_LEX *save_select= thd->lex->current_select;
thd->lex->current_select= select_lex;
if (join->prepare(select_lex->table_list.first,
select_lex->with_wild,
select_lex->where,
select_lex->order_list.elements +
select_lex->group_list.elements,
select_lex->order_list.first,
false,
select_lex->group_list.first,
select_lex->having,
NULL, select_lex,
select_lex->master_unit()))
return 1;
thd->lex->current_select= save_select;
return 0;
}
int subselect_union_engine::prepare(THD *thd_arg)
{
set_thd(thd_arg);
return unit->prepare(unit->derived, result, SELECT_NO_UNLOCK);
}
int subselect_uniquesubquery_engine::prepare(THD *)
{
/* Should never be called. */
DBUG_ASSERT(FALSE);
return 1;
}
/*
Check if last execution of the subquery engine produced any rows
SYNOPSIS
subselect_single_select_engine::no_rows()
DESCRIPTION
Check if last execution of the subquery engine produced any rows. The
return value is undefined if last execution ended in an error.
RETURN
TRUE - Last subselect execution has produced no rows
FALSE - Otherwise
*/
bool subselect_single_select_engine::no_rows()
{
return !item->assigned();
}
/**
Makes storage for the output values for the subquery and calcuates
their data and column types and their nullability.
*/
bool subselect_engine::set_row(List<Item> &item_list, Item_cache **row)
{
Item *sel_item;
List_iterator_fast<Item> li(item_list);
set_handler(&type_handler_varchar);
for (uint i= 0; (sel_item= li++); i++)
{
item->max_length= sel_item->max_length;
set_handler(sel_item->type_handler());
item->decimals= sel_item->decimals;
item->unsigned_flag= sel_item->unsigned_flag;
maybe_null= sel_item->maybe_null;
if (!(row[i]= sel_item->get_cache(thd)))
return TRUE;
row[i]->setup(thd, sel_item);
//psergey-backport-timours: row[i]->store(sel_item);
}
if (item_list.elements > 1)
set_handler(&type_handler_row);
return FALSE;
}
bool subselect_single_select_engine::fix_length_and_dec(Item_cache **row)
{
DBUG_ASSERT(row || select_lex->item_list.elements==1);
if (set_row(select_lex->item_list, row))
return TRUE;
item->collation.set(row[0]->collation);
if (cols() != 1)
maybe_null= 0;
return FALSE;
}
bool subselect_union_engine::fix_length_and_dec(Item_cache **row)
{
DBUG_ASSERT(row || unit->first_select()->item_list.elements==1);
if (unit->first_select()->item_list.elements == 1)
{
if (set_row(unit->types, row))
return TRUE;
item->collation.set(row[0]->collation);
}
else
{
bool maybe_null_saved= maybe_null;
if (set_row(unit->types, row))
return TRUE;
maybe_null= maybe_null_saved;
}
return FALSE;
}
bool subselect_uniquesubquery_engine::fix_length_and_dec(Item_cache **row)
{
//this never should be called
DBUG_ASSERT(0);
return FALSE;
}
int read_first_record_seq(JOIN_TAB *tab);
int rr_sequential(READ_RECORD *info);
int join_read_always_key_or_null(JOIN_TAB *tab);
int join_read_next_same_or_null(READ_RECORD *info);
int subselect_single_select_engine::exec()
{
DBUG_ENTER("subselect_single_select_engine::exec");
char const *save_where= thd->where;
SELECT_LEX *save_select= thd->lex->current_select;
thd->lex->current_select= select_lex;
if (join->optimization_state == JOIN::NOT_OPTIMIZED)
{
SELECT_LEX_UNIT *unit= select_lex->master_unit();
unit->set_limit(unit->global_parameters());
if (join->optimize())
{
thd->where= save_where;
executed= 1;
thd->lex->current_select= save_select;
DBUG_RETURN(join->error ? join->error : 1);
}
if (!select_lex->uncacheable && thd->lex->describe &&
!(join->select_options & SELECT_DESCRIBE))
{
item->update_used_tables();
if (item->const_item())
{
/*
It's necessary to keep original JOIN table because
create_sort_index() function may overwrite original
JOIN_TAB::type and wrong optimization method can be
selected on re-execution.
*/
select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
select_lex->master_unit()->uncacheable|= UNCACHEABLE_EXPLAIN;
}
}
if (item->engine_changed(this))
{
thd->lex->current_select= save_select;
DBUG_RETURN(1);
}
}
if (select_lex->uncacheable &&
select_lex->uncacheable != UNCACHEABLE_EXPLAIN
&& executed)
{
if (join->reinit())
{
thd->where= save_where;
thd->lex->current_select= save_select;
DBUG_RETURN(1);
}
item->reset();
item->assigned((executed= 0));
}
if (!executed)
{
item->reset_value_registration();
JOIN_TAB *changed_tabs[MAX_TABLES];
JOIN_TAB **last_changed_tab= changed_tabs;
if (item->have_guarded_conds())
{
/*
For at least one of the pushed predicates the following is true:
We should not apply optimizations based on the condition that was
pushed down into the subquery. Those optimizations are ref[_or_null]
accesses. Change them to be full table scans.
*/
JOIN_TAB *tab;
for (tab= first_linear_tab(join, WITH_BUSH_ROOTS, WITHOUT_CONST_TABLES);
tab; tab= next_linear_tab(join, tab, WITH_BUSH_ROOTS))
{
if (tab && tab->keyuse)
{
for (uint i= 0; i < tab->ref.key_parts; i++)
{
bool *cond_guard= tab->ref.cond_guards[i];
if (cond_guard && !*cond_guard)
{
/* Change the access method to full table scan */
tab->save_read_first_record= tab->read_first_record;
tab->save_read_record= tab->read_record.read_record_func;
tab->read_record.read_record_func= rr_sequential;
tab->read_first_record= read_first_record_seq;
tab->read_record.thd= join->thd;
tab->read_record.ref_length= tab->table->file->ref_length;
tab->read_record.unlock_row= rr_unlock_row;
*(last_changed_tab++)= tab;
break;
}
}
}
}
}
join->exec();
/* Enable the optimizations back */
for (JOIN_TAB **ptab= changed_tabs; ptab != last_changed_tab; ptab++)
{
JOIN_TAB *tab= *ptab;
tab->read_record.ref_length= 0;
tab->read_first_record= tab->save_read_first_record;
tab->read_record.read_record_func= tab->save_read_record;
}
executed= 1;
if (!(uncacheable() & ~UNCACHEABLE_EXPLAIN) &&
!item->with_recursive_reference)
item->make_const();
thd->where= save_where;
thd->lex->current_select= save_select;
DBUG_RETURN(join->error || thd->is_fatal_error || thd->is_error());
}
thd->where= save_where;
thd->lex->current_select= save_select;
DBUG_RETURN(0);
}
int subselect_union_engine::exec()
{
char const *save_where= thd->where;
int res= unit->exec();
thd->where= save_where;
return res;
}
/*
Search for at least one row satisfying select condition
SYNOPSIS
subselect_uniquesubquery_engine::scan_table()
DESCRIPTION
Scan the table using sequential access until we find at least one row
satisfying select condition.
The caller must set this->empty_result_set=FALSE before calling this
function. This function will set it to TRUE if it finds a matching row.
RETURN
FALSE - OK
TRUE - Error
*/
int subselect_uniquesubquery_engine::scan_table()
{
int error;
TABLE *table= tab->table;
DBUG_ENTER("subselect_uniquesubquery_engine::scan_table");
if ((table->file->inited &&
(error= table->file->ha_index_end())) ||
(error= table->file->ha_rnd_init(1)))
{
(void) report_error(table, error);
DBUG_RETURN(true);
}
table->file->extra_opt(HA_EXTRA_CACHE,
get_thd()->variables.read_buff_size);
table->null_row= 0;
for (;;)
{
error=table->file->ha_rnd_next(table->record[0]);
if (unlikely(error))
{
if (error == HA_ERR_END_OF_FILE)
{
error= 0;
break;
}
else
{
error= report_error(table, error);
break;
}
}
if (!cond || cond->val_int())
{
empty_result_set= FALSE;
break;
}
}
table->file->ha_rnd_end();
DBUG_RETURN(error != 0);
}
/**
Copy ref key for index access into the only subquery table.
@details
Copy ref key and check for conversion problems.
If there is an error converting the left IN operand to the column type of
the right IN operand count it as no match. In this case IN has the value of
FALSE. We mark the subquery table cursor as having no more rows (to ensure
that the processing that follows will not find a match) and return FALSE,
so IN is not treated as returning NULL.
@returns
@retval FALSE The outer ref was copied into an index lookup key.
@retval TRUE The outer ref cannot possibly match any row, IN is FALSE.
*/
bool subselect_uniquesubquery_engine::copy_ref_key(bool skip_constants)
{
DBUG_ENTER("subselect_uniquesubquery_engine::copy_ref_key");
for (store_key **copy= tab->ref.key_copy ; *copy ; copy++)
{
enum store_key::store_key_result store_res;
if (skip_constants && (*copy)->store_key_is_const())
continue;
store_res= (*copy)->copy();
tab->ref.key_err= store_res;
if (store_res == store_key::STORE_KEY_FATAL)
{
/*
Error converting the left IN operand to the column type of the right
IN operand.
*/
DBUG_RETURN(true);
}
}
DBUG_RETURN(false);
}
/**
Execute subselect via unique index lookup
@details
Find rows corresponding to the ref key using index access.
If some part of the lookup key is NULL, then we're evaluating
NULL IN (SELECT ... )
This is a special case, we don't need to search for NULL in the table,
instead, the result value is
- NULL if select produces empty row set
- FALSE otherwise.
In some cases (IN subselect is a top level item, i.e. abort_on_null==TRUE)
the caller doesn't distinguish between NULL and FALSE result and we just
return FALSE.
Otherwise we make a full table scan to see if there is at least one
matching row.
The result of this function (info about whether a row was found) is
stored in this->empty_result_set.
@returns
@retval 0 OK
@retval 1 notify caller to call Item_subselect::reset(),
in most cases reset() sets the result to NULL
*/
int subselect_uniquesubquery_engine::exec()
{
DBUG_ENTER("subselect_uniquesubquery_engine::exec");
int error;
TABLE *table= tab->table;
empty_result_set= TRUE;
table->status= 0;
Item_in_subselect *in_subs= (Item_in_subselect *) item;
if (!tab->preread_init_done && tab->preread_init())
DBUG_RETURN(1);
if (in_subs->left_expr_has_null())
{
/*
The case when all values in left_expr are NULL is handled by
Item_in_optimizer::val_int().
*/
if (in_subs->is_top_level_item())
DBUG_RETURN(1); /* notify caller to call reset() and set NULL value. */
else
DBUG_RETURN(scan_table());
}
if (copy_ref_key(true))
{
/* We know that there will be no rows even if we scan. */
in_subs->value= 0;
DBUG_RETURN(0);
}
if (!table->file->inited &&
(error= table->file->ha_index_init(tab->ref.key, 0)))
{
(void) report_error(table, error);
DBUG_RETURN(true);
}
error= table->file->ha_index_read_map(table->record[0],
tab->ref.key_buff,
make_prev_keypart_map(tab->
ref.key_parts),
HA_READ_KEY_EXACT);
if (unlikely(error &&
error != HA_ERR_KEY_NOT_FOUND && error != HA_ERR_END_OF_FILE))
error= report_error(table, error);
else
{
error= 0;
table->null_row= 0;
if (!table->status && (!cond || cond->val_int()))
{
((Item_in_subselect *) item)->value= 1;
empty_result_set= FALSE;
}
else
((Item_in_subselect *) item)->value= 0;
}
DBUG_RETURN(error != 0);
}
/*
TIMOUR: write comment
*/
int subselect_uniquesubquery_engine::index_lookup()
{
DBUG_ENTER("subselect_uniquesubquery_engine::index_lookup");
int error;
TABLE *table= tab->table;
if (!table->file->inited)
table->file->ha_index_init(tab->ref.key, 0);
error= table->file->ha_index_read_map(table->record[0],
tab->ref.key_buff,
make_prev_keypart_map(tab->
ref.key_parts),
HA_READ_KEY_EXACT);
DBUG_PRINT("info", ("lookup result: %i", error));
if (unlikely(error && error != HA_ERR_KEY_NOT_FOUND &&
error != HA_ERR_END_OF_FILE))
{
/*
TIMOUR: I don't understand at all when do we need to call report_error.
In most places where we access an index, we don't do this. Why here?
*/
error= report_error(table, error);
DBUG_RETURN(error);
}
table->null_row= 0;
if (!error && (!cond || cond->val_int()))
((Item_in_subselect *) item)->value= 1;
else
((Item_in_subselect *) item)->value= 0;
DBUG_RETURN(0);
}
subselect_uniquesubquery_engine::~subselect_uniquesubquery_engine()
{
/* Tell handler we don't need the index anymore */
//psergey-merge-todo: the following was gone in 6.0:
//psergey-merge: don't need this after all: tab->table->file->ha_index_end();
}
/**
Execute subselect via unique index lookup
@details
The engine is used to resolve subqueries in form
oe IN (SELECT key FROM tbl WHERE subq_where)
The value of the predicate is calculated as follows:
1. If oe IS NULL, this is a special case, do a full table scan on
table tbl and search for row that satisfies subq_where. If such
row is found, return NULL, otherwise return FALSE.
2. Make an index lookup via key=oe, search for a row that satisfies
subq_where. If found, return TRUE.
3. If check_null==TRUE, make another lookup via key=NULL, search for a
row that satisfies subq_where. If found, return NULL, otherwise
return FALSE.
@todo
The step #1 can be optimized further when the index has several key
parts. Consider a subquery:
(oe1, oe2) IN (SELECT keypart1, keypart2 FROM tbl WHERE subq_where)
and suppose we need to evaluate it for {oe1, oe2}=={const1, NULL}.
Current code will do a full table scan and obtain correct result. There
is a better option: instead of evaluating
SELECT keypart1, keypart2 FROM tbl WHERE subq_where (1)
and checking if it has produced any matching rows, evaluate
SELECT keypart2 FROM tbl WHERE subq_where AND keypart1=const1 (2)
If this query produces a row, the result is NULL (as we're evaluating
"(const1, NULL) IN { (const1, X), ... }", which has a value of UNKNOWN,
i.e. NULL). If the query produces no rows, the result is FALSE.
We currently evaluate (1) by doing a full table scan. (2) can be
evaluated by doing a "ref" scan on "keypart1=const1", which can be much
cheaper. We can use index statistics to quickly check whether "ref" scan
will be cheaper than full table scan.
@returns
@retval 0 OK
@retval 1 notify caller to call Item_subselect::reset(),
in most cases reset() sets the result to NULL
*/
int subselect_indexsubquery_engine::exec()
{
DBUG_ENTER("subselect_indexsubquery_engine");
int error;
bool null_finding= 0;
TABLE *table= tab->table;
Item_in_subselect *in_subs= (Item_in_subselect *) item;
((Item_in_subselect *) item)->value= 0;
empty_result_set= TRUE;
table->status= 0;
if (check_null)
{
/* We need to check for NULL if there wasn't a matching value */
*tab->ref.null_ref_key= 0; // Search first for not null
((Item_in_subselect *) item)->was_null= 0;
}
if (!tab->preread_init_done && tab->preread_init())
DBUG_RETURN(1);
if (in_subs->left_expr_has_null())
{
/*
The case when all values in left_expr are NULL is handled by
Item_in_optimizer::val_int().
*/
if (in_subs->is_top_level_item())
DBUG_RETURN(1); /* notify caller to call reset() and set NULL value. */
else
DBUG_RETURN(scan_table());
}
if (copy_ref_key(true))
{
/* We know that there will be no rows even if we scan. */
in_subs->value= 0;
DBUG_RETURN(0);
}
if (!table->file->inited &&
(error= table->file->ha_index_init(tab->ref.key, 1)))
{
(void) report_error(table, error);
DBUG_RETURN(true);
}
error= table->file->ha_index_read_map(table->record[0],
tab->ref.key_buff,
make_prev_keypart_map(tab->
ref.key_parts),
HA_READ_KEY_EXACT);
if (unlikely(error &&
error != HA_ERR_KEY_NOT_FOUND && error != HA_ERR_END_OF_FILE))
error= report_error(table, error);
else
{
for (;;)
{
error= 0;
table->null_row= 0;
if (!table->status)
{
if ((!cond || cond->val_int()) && (!having || having->val_int()))
{
empty_result_set= FALSE;
if (null_finding)
((Item_in_subselect *) item)->was_null= 1;
else
((Item_in_subselect *) item)->value= 1;
break;
}
error= table->file->ha_index_next_same(table->record[0],
tab->ref.key_buff,
tab->ref.key_length);
if (unlikely(error && error != HA_ERR_END_OF_FILE))
{
error= report_error(table, error);
break;
}
}
else
{
if (!check_null || null_finding)
break; /* We don't need to check nulls */
*tab->ref.null_ref_key= 1;
null_finding= 1;
/* Check if there exists a row with a null value in the index */
if (unlikely((error= (safe_index_read(tab) == 1))))
break;
}
}
}
DBUG_RETURN(error != 0);
}
uint subselect_single_select_engine::cols() const
{
//psergey-sj-backport: the following assert was gone in 6.0:
//DBUG_ASSERT(select_lex->join != 0); // should be called after fix_fields()
//return select_lex->join->fields_list.elements;
return select_lex->item_list.elements;
}
uint subselect_union_engine::cols() const
{
DBUG_ASSERT(unit->is_prepared()); // should be called after fix_fields()
return unit->types.elements;
}
uint8 subselect_single_select_engine::uncacheable()
{
return select_lex->uncacheable;
}
uint8 subselect_union_engine::uncacheable()
{
return unit->uncacheable;
}
void subselect_single_select_engine::exclude()
{
select_lex->master_unit()->exclude_level();
}
void subselect_union_engine::exclude()
{
unit->exclude_level();
}
void subselect_uniquesubquery_engine::exclude()
{
//this never should be called
DBUG_ASSERT(0);
}
table_map subselect_engine::calc_const_tables(List<TABLE_LIST> &list)
{
table_map map= 0;
List_iterator<TABLE_LIST> ti(list);
TABLE_LIST *table;
//for (; table; table= table->next_leaf)
while ((table= ti++))
{
TABLE *tbl= table->table;
if (tbl && tbl->const_table)
map|= tbl->map;
}
return map;
}
table_map subselect_single_select_engine::upper_select_const_tables()
{
return calc_const_tables(select_lex->outer_select()->leaf_tables);
}
table_map subselect_union_engine::upper_select_const_tables()
{
return calc_const_tables(unit->outer_select()->leaf_tables);
}
void subselect_single_select_engine::print(String *str,
enum_query_type query_type)
{
With_clause* with_clause= select_lex->get_with_clause();
if (with_clause)
with_clause->print(str, query_type);
select_lex->print(get_thd(), str, query_type);
}
void subselect_union_engine::print(String *str, enum_query_type query_type)
{
unit->print(str, query_type);
}
void subselect_uniquesubquery_engine::print(String *str,
enum_query_type query_type)
{
str->append(STRING_WITH_LEN("<primary_index_lookup>("));
tab->ref.items[0]->print(str, query_type);
str->append(STRING_WITH_LEN(" in "));
if (tab->table->s->table_category == TABLE_CATEGORY_TEMPORARY)
{
/*
Temporary tables' names change across runs, so they can't be used for
EXPLAIN EXTENDED.
*/
str->append(STRING_WITH_LEN("<temporary table>"));
}
else
str->append(&tab->table->s->table_name);
KEY *key_info= tab->table->key_info+ tab->ref.key;
str->append(STRING_WITH_LEN(" on "));
str->append(&key_info->name);
if (cond)
{
str->append(STRING_WITH_LEN(" where "));
cond->print(str, query_type);
}
str->append(')');
}
/*
TODO:
The above ::print method should be changed as below. Do it after
all other tests pass.
void subselect_uniquesubquery_engine::print(String *str)
{
KEY *key_info= tab->table->key_info + tab->ref.key;
str->append(STRING_WITH_LEN("<primary_index_lookup>("));
for (uint i= 0; i < key_info->user_defined_key_parts; i++)
tab->ref.items[i]->print(str);
str->append(STRING_WITH_LEN(" in "));
str->append(&tab->table->s->table_name);
str->append(STRING_WITH_LEN(" on "));
str->append(&key_info->name);
if (cond)
{
str->append(STRING_WITH_LEN(" where "));
cond->print(str);
}
str->append(')');
}
*/
void subselect_indexsubquery_engine::print(String *str,
enum_query_type query_type)
{
str->append(STRING_WITH_LEN("<index_lookup>("));
tab->ref.items[0]->print(str, query_type);
str->append(STRING_WITH_LEN(" in "));
str->append(tab->table->s->table_name.str, tab->table->s->table_name.length);
KEY *key_info= tab->table->key_info+ tab->ref.key;
str->append(STRING_WITH_LEN(" on "));
str->append(&key_info->name);
if (check_null)
str->append(STRING_WITH_LEN(" checking NULL"));
if (cond)
{
str->append(STRING_WITH_LEN(" where "));
cond->print(str, query_type);
}
if (having)
{
str->append(STRING_WITH_LEN(" having "));
having->print(str, query_type);
}
str->append(')');
}
/**
change select_result object of engine.
@param si new subselect Item
@param res new select_result object
@param temp temporary assignment
@retval
FALSE OK
@retval
TRUE error
*/
bool
subselect_single_select_engine::change_result(Item_subselect *si,
select_result_interceptor *res,
bool temp)
{
DBUG_ENTER("subselect_single_select_engine::change_result");
item= si;
if (temp)
{
/*
Here we reuse change_item_tree to roll back assignment. It has
nothing special about Item* pointer so it is safe conversion. We do
not change the interface to be compatible with MySQL.
*/
thd->change_item_tree((Item**) &result, (Item*)res);
}
else
result= res;
/*
We can't use 'result' below as gcc 4.2.4's alias optimization
assumes that result was not changed by thd->change_item_tree().
I tried to find a solution to make gcc happy, but could not find anything
that would not require a lot of extra code that would be harder to manage
than the current code.
*/
DBUG_RETURN(select_lex->join->change_result(res, NULL));
}
/**
change select_result object of engine.
@param si new subselect Item
@param res new select_result object
@retval
FALSE OK
@retval
TRUE error
*/
bool subselect_union_engine::change_result(Item_subselect *si,
select_result_interceptor *res,
bool temp)
{
item= si;
int rc= unit->change_result(res, result);
if (temp)
thd->change_item_tree((Item**) &result, (Item*)res);
else
result= res;
return rc;
}
/**
change select_result emulation, never should be called.
@param si new subselect Item
@param res new select_result object
@retval
FALSE OK
@retval
TRUE error
*/
bool
subselect_uniquesubquery_engine::change_result(Item_subselect *si,
select_result_interceptor *res,
bool temp
__attribute__((unused)))
{
DBUG_ASSERT(0);
return TRUE;
}
/**
Report about presence of tables in subquery.
@retval
TRUE there are not tables used in subquery
@retval
FALSE there are some tables in subquery
*/
bool subselect_single_select_engine::no_tables()
{
return(select_lex->table_list.elements == 0);
}
/*
Check statically whether the subquery can return NULL
SINOPSYS
subselect_single_select_engine::may_be_null()
RETURN
FALSE can guarantee that the subquery never return NULL
TRUE otherwise
*/
bool subselect_single_select_engine::may_be_null()
{
return ((no_tables() && !join->conds && !join->having) ? maybe_null : 1);
}
/**
Report about presence of tables in subquery.
@retval
TRUE there are not tables used in subquery
@retval
FALSE there are some tables in subquery
*/
bool subselect_union_engine::no_tables()
{
for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
{
if (sl->table_list.elements)
return FALSE;
}
return TRUE;
}
/**
Report about presence of tables in subquery.
@retval
TRUE there are not tables used in subquery
@retval
FALSE there are some tables in subquery
*/
bool subselect_uniquesubquery_engine::no_tables()
{
/* returning value is correct, but this method should never be called */
DBUG_ASSERT(FALSE);
return 0;
}
/******************************************************************************
WL#1110 - Implementation of class subselect_hash_sj_engine
******************************************************************************/
/**
Check if an IN predicate should be executed via partial matching using
only schema information.
@details
This test essentially has three results:
- partial matching is applicable, but cannot be executed due to a
limitation in the total number of indexes, as a result we can't
use subquery materialization at all.
- partial matching is either applicable or not, and this can be
determined by looking at 'this->max_keys'.
If max_keys > 1, then we need partial matching because there are
more indexes than just the one we use during materialization to
remove duplicates.
@note
TIMOUR: The schema-based analysis for partial matching can be done once for
prepared statement and remembered. It is done here to remove the need to
save/restore all related variables between each re-execution, thus making
the code simpler.
@retval PARTIAL_MATCH if a partial match should be used
@retval COMPLETE_MATCH if a complete match (index lookup) should be used
*/
subselect_hash_sj_engine::exec_strategy
subselect_hash_sj_engine::get_strategy_using_schema()
{
Item_in_subselect *item_in= (Item_in_subselect *) item;
if (item_in->is_top_level_item())
return COMPLETE_MATCH;
else
{
List_iterator<Item> inner_col_it(*item_in->unit->get_column_types(false));
Item *outer_col, *inner_col;
for (uint i= 0; i < item_in->left_expr->cols(); i++)
{
outer_col= item_in->left_expr->element_index(i);
inner_col= inner_col_it++;
if (!inner_col->maybe_null && !outer_col->maybe_null)
bitmap_set_bit(&non_null_key_parts, i);
else
{
bitmap_set_bit(&partial_match_key_parts, i);
++count_partial_match_columns;
}
}
}
/* If no column contains NULLs use regular hash index lookups. */
if (count_partial_match_columns)
return PARTIAL_MATCH;
return COMPLETE_MATCH;
}
/**
Test whether an IN predicate must be computed via partial matching
based on the NULL statistics for each column of a materialized subquery.
@details The procedure analyzes column NULL statistics, updates the
matching type of columns that cannot be NULL or that contain only NULLs.
Based on this, the procedure determines the final execution strategy for
the [NOT] IN predicate.
@retval PARTIAL_MATCH if a partial match should be used
@retval COMPLETE_MATCH if a complete match (index lookup) should be used
*/
subselect_hash_sj_engine::exec_strategy
subselect_hash_sj_engine::get_strategy_using_data()
{
Item_in_subselect *item_in= (Item_in_subselect *) item;
select_materialize_with_stats *result_sink=
(select_materialize_with_stats *) result;
Item *outer_col;
/*
If we already determined that a complete match is enough based on schema
information, nothing can be better.
*/
if (strategy == COMPLETE_MATCH)
return COMPLETE_MATCH;
for (uint i= 0; i < item_in->left_expr->cols(); i++)
{
if (!bitmap_is_set(&partial_match_key_parts, i))
continue;
outer_col= item_in->left_expr->element_index(i);
/*
If column 'i' doesn't contain NULLs, and the corresponding outer reference
cannot have a NULL value, then 'i' is a non-nullable column.
*/
if (result_sink->get_null_count_of_col(i) == 0 && !outer_col->maybe_null)
{
bitmap_clear_bit(&partial_match_key_parts, i);
bitmap_set_bit(&non_null_key_parts, i);
--count_partial_match_columns;
}
if (result_sink->get_null_count_of_col(i) == tmp_table->file->stats.records)
++count_null_only_columns;
if (result_sink->get_null_count_of_col(i))
++count_columns_with_nulls;
}
/* If no column contains NULLs use regular hash index lookups. */
if (!count_partial_match_columns)
return COMPLETE_MATCH;
return PARTIAL_MATCH;
}
void
subselect_hash_sj_engine::choose_partial_match_strategy(
bool has_non_null_key, bool has_covering_null_row,
MY_BITMAP *partial_match_key_parts_arg)
{
ulonglong pm_buff_size;
DBUG_ASSERT(strategy == PARTIAL_MATCH);
/*
Choose according to global optimizer switch. If only one of the switches is
'ON', then the remaining strategy is the only possible one. The only cases
when this will be overridden is when the total size of all buffers for the
merge strategy is bigger than the 'rowid_merge_buff_size' system variable,
or if there isn't enough physical memory to allocate the buffers.
*/
if (!optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE) &&
optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN))
strategy= PARTIAL_MATCH_SCAN;
else if
( optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE) &&
!optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN))
strategy= PARTIAL_MATCH_MERGE;
/*
If both switches are ON, or both are OFF, we interpret that as "let the
optimizer decide". Perform a cost based choice between the two partial
matching strategies.
*/
/*
TIMOUR: the above interpretation of the switch values could be changed to:
- if both are ON - let the optimizer decide,
- if both are OFF - do not use partial matching, therefore do not use
materialization in non-top-level predicates.
The problem with this is that we know for sure if we need partial matching
only after the subquery is materialized, and this is too late to revert to
the IN=>EXISTS strategy.
*/
if (strategy == PARTIAL_MATCH)
{
/*
TIMOUR: Currently we use a super simplistic measure. This will be
addressed in a separate task.
*/
if (tmp_table->file->stats.records < 100)
strategy= PARTIAL_MATCH_SCAN;
else
strategy= PARTIAL_MATCH_MERGE;
}
/* Check if there is enough memory for the rowid merge strategy. */
if (strategy == PARTIAL_MATCH_MERGE)
{
pm_buff_size= rowid_merge_buff_size(has_non_null_key,
has_covering_null_row,
partial_match_key_parts_arg);
if (pm_buff_size > thd->variables.rowid_merge_buff_size)
strategy= PARTIAL_MATCH_SCAN;
}
}
/*
Compute the memory size of all buffers proportional to the number of rows
in tmp_table.
@details
If the result is bigger than thd->variables.rowid_merge_buff_size, partial
matching via merging is not applicable.
*/
ulonglong subselect_hash_sj_engine::rowid_merge_buff_size(
bool has_non_null_key, bool has_covering_null_row,
MY_BITMAP *partial_match_key_parts)
{
/* Total size of all buffers used by partial matching. */
ulonglong buff_size;
ha_rows row_count= tmp_table->file->stats.records;
uint rowid_length= tmp_table->file->ref_length;
select_materialize_with_stats *result_sink=
(select_materialize_with_stats *) result;
ha_rows max_null_row;
/* Size of the subselect_rowid_merge_engine::row_num_to_rowid buffer. */
buff_size= row_count * rowid_length * sizeof(uchar);
if (has_non_null_key)
{
/* Add the size of Ordered_key::key_buff of the only non-NULL key. */
buff_size+= row_count * sizeof(rownum_t);
}
if (!has_covering_null_row)
{
for (uint i= 0; i < partial_match_key_parts->n_bits; i++)
{
if (!bitmap_is_set(partial_match_key_parts, i) ||
result_sink->get_null_count_of_col(i) == row_count)
continue; /* In these cases we wouldn't construct Ordered keys. */
/* Add the size of Ordered_key::key_buff */
buff_size+= (row_count - result_sink->get_null_count_of_col(i)) *
sizeof(rownum_t);
/* Add the size of Ordered_key::null_key */
max_null_row= result_sink->get_max_null_of_col(i);
if (max_null_row >= UINT_MAX)
{
/*
There can be at most UINT_MAX bits in a MY_BITMAP that is used to
store NULLs in an Ordered_key. Return a number of bytes bigger than
the maximum allowed memory buffer for partial matching to disable
the rowid merge strategy.
*/
return ULONGLONG_MAX;
}
buff_size+= bitmap_buffer_size(max_null_row);
}
}
return buff_size;
}
/*
Initialize a MY_BITMAP with a buffer allocated on the current
memory root.
TIMOUR: move to bitmap C file?
*/
static my_bool
my_bitmap_init_memroot(MY_BITMAP *map, uint n_bits, MEM_ROOT *mem_root)
{
my_bitmap_map *bitmap_buf;
if (!(bitmap_buf= (my_bitmap_map*) alloc_root(mem_root,
bitmap_buffer_size(n_bits))) ||
my_bitmap_init(map, bitmap_buf, n_bits, FALSE))
return TRUE;
bitmap_clear_all(map);
return FALSE;
}
/**
Create all structures needed for IN execution that can live between PS
reexecution.
@param tmp_columns the items that produce the data for the temp table
@param subquery_id subquery's identifier (to make "<subquery%d>" name for
EXPLAIN)
@details
- Create a temporary table to store the result of the IN subquery. The
temporary table has one hash index on all its columns.
- Create a new result sink that sends the result stream of the subquery to
the temporary table,
@notice:
Currently Item_subselect::init() already chooses and creates at parse
time an engine with a corresponding JOIN to execute the subquery.
@retval TRUE if error
@retval FALSE otherwise
*/
bool subselect_hash_sj_engine::init(List<Item> *tmp_columns, uint subquery_id)
{
THD *thd= get_thd();
select_unit *result_sink;
/* Options to create_tmp_table. */
ulonglong tmp_create_options= thd->variables.option_bits | TMP_TABLE_ALL_COLUMNS;
/* | TMP_TABLE_FORCE_MYISAM; TIMOUR: force MYISAM */
DBUG_ENTER("subselect_hash_sj_engine::init");
if (my_bitmap_init_memroot(&non_null_key_parts, tmp_columns->elements,
thd->mem_root) ||
my_bitmap_init_memroot(&partial_match_key_parts, tmp_columns->elements,
thd->mem_root))
DBUG_RETURN(TRUE);
/*
Create and initialize a select result interceptor that stores the
result stream in a temporary table. The temporary table itself is
managed (created/filled/etc) internally by the interceptor.
*/
/*
TIMOUR:
Select a more efficient result sink when we know there is no need to collect
data statistics.
if (strategy == COMPLETE_MATCH)
{
if (!(result= new select_union))
DBUG_RETURN(TRUE);
}
else if (strategy == PARTIAL_MATCH)
{
if (!(result= new select_materialize_with_stats))
DBUG_RETURN(TRUE);
}
*/
if (!(result_sink= new (thd->mem_root) select_materialize_with_stats(thd)))
DBUG_RETURN(TRUE);
char buf[32];
LEX_CSTRING name;
name.length= my_snprintf(buf, sizeof(buf), "<subquery%u>", subquery_id);
if (!(name.str= (char*) thd->memdup(buf, name.length + 1)))
DBUG_RETURN(TRUE);
result_sink->get_tmp_table_param()->materialized_subquery= true;
if (item->substype() == Item_subselect::IN_SUBS &&
((Item_in_subselect*)item)->is_jtbm_merged)
{
result_sink->get_tmp_table_param()->force_not_null_cols= true;
}
if (result_sink->create_result_table(thd, tmp_columns, TRUE,
tmp_create_options,
&name, TRUE, TRUE, FALSE, 0))
DBUG_RETURN(TRUE);
tmp_table= result_sink->table;
result= result_sink;
/*
If the subquery has blobs, or the total key length is bigger than
some length, or the total number of key parts is more than the
allowed maximum (currently MAX_REF_PARTS == 32), then the created
index cannot be used for lookups and we can't use hash semi
join. If this is the case, delete the temporary table since it
will not be used, and tell the caller we failed to initialize the
engine.
*/
if (tmp_table->s->keys == 0)
{
//fprintf(stderr, "Q: %s\n", current_thd->query());
DBUG_ASSERT(0);
DBUG_ASSERT(
tmp_table->s->uniques ||
tmp_table->key_info->key_length >= tmp_table->file->max_key_length() ||
tmp_table->key_info->user_defined_key_parts >
tmp_table->file->max_key_parts());
free_tmp_table(thd, tmp_table);
tmp_table= NULL;
delete result;
result= NULL;
DBUG_RETURN(TRUE);
}
/*
Make sure there is only one index on the temp table, and it doesn't have
the extra key part created when s->uniques > 0.
*/
DBUG_ASSERT(tmp_table->s->keys == 1 &&
((Item_in_subselect *) item)->left_expr->cols() ==
tmp_table->key_info->user_defined_key_parts);
if (make_semi_join_conds() ||
/* A unique_engine is used both for complete and partial matching. */
!(lookup_engine= make_unique_engine()))
DBUG_RETURN(TRUE);
/*
Repeat name resolution for 'cond' since cond is not part of any
clause of the query, and it is not 'fixed' during JOIN::prepare.
*/
if (semi_join_conds &&
semi_join_conds->fix_fields_if_needed(thd, (Item**)&semi_join_conds))
DBUG_RETURN(TRUE);
/* Let our engine reuse this query plan for materialization. */
materialize_join= materialize_engine->join;
materialize_join->change_result(result, NULL);
DBUG_RETURN(FALSE);
}
/*
Create an artificial condition to post-filter those rows matched by index
lookups that cannot be distinguished by the index lookup procedure.
@notes
The need for post-filtering may occur e.g. because of
truncation. Prepared statements execution requires that fix_fields is
called for every execution. In order to call fix_fields we need to
create a Name_resolution_context and a corresponding TABLE_LIST for
the temporary table for the subquery, so that all column references
to the materialized subquery table can be resolved correctly.
@returns
@retval TRUE memory allocation error occurred
@retval FALSE the conditions were created and resolved (fixed)
*/
bool subselect_hash_sj_engine::make_semi_join_conds()
{
/*
Table reference for tmp_table that is used to resolve column references
(Item_fields) to columns in tmp_table.
*/
TABLE_LIST *tmp_table_ref;
/* Name resolution context for all tmp_table columns created below. */
Name_resolution_context *context;
Item_in_subselect *item_in= (Item_in_subselect *) item;
LEX_CSTRING table_name;
DBUG_ENTER("subselect_hash_sj_engine::make_semi_join_conds");
DBUG_ASSERT(semi_join_conds == NULL);
if (!(semi_join_conds= new (thd->mem_root) Item_cond_and(thd)))
DBUG_RETURN(TRUE);
if (!(tmp_table_ref= (TABLE_LIST*) thd->alloc(sizeof(TABLE_LIST))))
DBUG_RETURN(TRUE);
table_name.str= tmp_table->alias.c_ptr();
table_name.length= tmp_table->alias.length(),
tmp_table_ref->init_one_table(&empty_clex_str, &table_name, NULL, TL_READ);
tmp_table_ref->table= tmp_table;
context= new Name_resolution_context;
context->init();
context->first_name_resolution_table=
context->last_name_resolution_table= tmp_table_ref;
semi_join_conds_context= context;
for (uint i= 0; i < item_in->left_expr->cols(); i++)
{
/* New equi-join condition for the current column. */
Item_func_eq *eq_cond;
/* Item for the corresponding field from the materialized temp table. */
Item_field *right_col_item;
if (!(right_col_item= new (thd->mem_root)
Item_temptable_field(thd, context, tmp_table->field[i])) ||
!(eq_cond= new (thd->mem_root)
Item_func_eq(thd, item_in->left_expr->element_index(i),
right_col_item)) ||
(((Item_cond_and*)semi_join_conds)->add(eq_cond, thd->mem_root)))
{
delete semi_join_conds;
semi_join_conds= NULL;
DBUG_RETURN(TRUE);
}
}
if (semi_join_conds->fix_fields(thd, (Item**)&semi_join_conds))
DBUG_RETURN(TRUE);
DBUG_RETURN(FALSE);
}
/**
Create a new uniquesubquery engine for the execution of an IN predicate.
@details
Create and initialize a new JOIN_TAB, and Table_ref objects to perform
lookups into the indexed temporary table.
@retval A new subselect_hash_sj_engine object
@retval NULL if a memory allocation error occurs
*/
subselect_uniquesubquery_engine*
subselect_hash_sj_engine::make_unique_engine()
{
Item_in_subselect *item_in= (Item_in_subselect *) item;
Item_iterator_row it(item_in->left_expr);
/* The only index on the temporary table. */
KEY *tmp_key= tmp_table->key_info;
JOIN_TAB *tab;
DBUG_ENTER("subselect_hash_sj_engine::make_unique_engine");
/*
Create and initialize the JOIN_TAB that represents an index lookup
plan operator into the materialized subquery result. Notice that:
- this JOIN_TAB has no corresponding JOIN (and doesn't need one), and
- here we initialize only those members that are used by
subselect_uniquesubquery_engine, so these objects are incomplete.
*/
if (!(tab= (JOIN_TAB*) thd->alloc(sizeof(JOIN_TAB))))
DBUG_RETURN(NULL);
tab->table= tmp_table;
tab->preread_init_done= FALSE;
tab->ref.tmp_table_index_lookup_init(thd, tmp_key, it, FALSE);
DBUG_RETURN(new subselect_uniquesubquery_engine(thd, tab, item,
semi_join_conds));
}
subselect_hash_sj_engine::~subselect_hash_sj_engine()
{
delete lookup_engine;
delete result;
if (tmp_table)
free_tmp_table(thd, tmp_table);
}
int subselect_hash_sj_engine::prepare(THD *thd_arg)
{
/*
Create and optimize the JOIN that will be used to materialize
the subquery if not yet created.
*/
set_thd(thd_arg);
return materialize_engine->prepare(thd);
}
/**
Cleanup performed after each PS execution.
@details
Called in the end of JOIN::prepare for PS from Item_subselect::cleanup.
*/
void subselect_hash_sj_engine::cleanup()
{
enum_engine_type lookup_engine_type= lookup_engine->engine_type();
is_materialized= FALSE;
bitmap_clear_all(&non_null_key_parts);
bitmap_clear_all(&partial_match_key_parts);
count_partial_match_columns= 0;
count_null_only_columns= 0;
strategy= UNDEFINED;
materialize_engine->cleanup();
/*
Restore the original Item_in_subselect engine. This engine is created once
at parse time and stored across executions, while all other materialization
related engines are created and chosen for each execution.
*/
((Item_in_subselect *) item)->engine= materialize_engine;
if (lookup_engine_type == TABLE_SCAN_ENGINE ||
lookup_engine_type == ROWID_MERGE_ENGINE)
{
subselect_engine *inner_lookup_engine;
inner_lookup_engine=
((subselect_partial_match_engine*) lookup_engine)->lookup_engine;
/*
Partial match engines are recreated for each PS execution inside
subselect_hash_sj_engine::exec().
*/
delete lookup_engine;
lookup_engine= inner_lookup_engine;
}
DBUG_ASSERT(lookup_engine->engine_type() == UNIQUESUBQUERY_ENGINE);
lookup_engine->cleanup();
result->cleanup(); /* Resets the temp table as well. */
DBUG_ASSERT(tmp_table);
free_tmp_table(thd, tmp_table);
tmp_table= NULL;
}
/*
Get fanout produced by tables specified in the table_map
*/
double get_fanout_with_deps(JOIN *join, table_map tset)
{
/* Handle the case of "Impossible WHERE" */
if (join->table_count == 0)
return 0.0;
/* First, recursively get all tables we depend on */
table_map deps_to_check= tset;
table_map checked_deps= 0;
table_map further_deps;
do
{
further_deps= 0;
Table_map_iterator tm_it(deps_to_check);
int tableno;
while ((tableno = tm_it.next_bit()) != Table_map_iterator::BITMAP_END)
{
/* get tableno's dependency tables that are not in needed_set */
further_deps |= join->map2table[tableno]->ref.depend_map & ~checked_deps;
}
checked_deps |= deps_to_check;
deps_to_check= further_deps;
} while (further_deps != 0);
/* Now, walk the join order and calculate the fanout */
double fanout= 1;
for (JOIN_TAB *tab= first_top_level_tab(join, WITHOUT_CONST_TABLES); tab;
tab= next_top_level_tab(join, tab))
{
/*
Ignore SJM nests. They have tab->table==NULL. There is no point to walk
inside them, because GROUP BY clause cannot refer to tables from within
subquery.
*/
if (!tab->is_sjm_nest() && (tab->table->map & checked_deps) &&
!tab->emb_sj_nest &&
tab->records_read != 0)
{
fanout *= tab->records_read;
}
}
return fanout;
}
#if 0
void check_out_index_stats(JOIN *join)
{
ORDER *order;
uint n_order_items;
/*
First, collect the keys that we can use in each table.
We can use a key if
- all tables refer to it.
*/
key_map key_start_use[MAX_TABLES];
key_map key_infix_use[MAX_TABLES];
table_map key_used=0;
table_map non_key_used= 0;
bzero(&key_start_use, sizeof(key_start_use)); //psergey-todo: safe initialization!
bzero(&key_infix_use, sizeof(key_infix_use));
for (order= join->group_list; order; order= order->next)
{
Item *item= order->item[0];
if (item->real_type() == Item::FIELD_ITEM)
{
if (item->used_tables() & OUTER_REF_TABLE_BIT)
continue; /* outside references are like constants for us */
Field *field= ((Item_field*)item->real_item())->field;
uint table_no= field->table->tablenr;
if (!(non_key_used && table_map(1) << table_no) &&
!field->part_of_key.is_clear_all())
{
key_map infix_map= field->part_of_key;
infix_map.subtract(field->key_start);
key_start_use[table_no].merge(field->key_start);
key_infix_use[table_no].merge(infix_map);
key_used |= table_no;
}
continue;
}
/*
Note: the below will cause clauses like GROUP BY YEAR(date) not to be
handled.
*/
non_key_used |= item->used_tables();
}
Table_map_iterator tm_it(key_used & ~non_key_used);
int tableno;
while ((tableno = tm_it.next_bit()) != Table_map_iterator::BITMAP_END)
{
key_map::iterator key_it(key_start_use);
int keyno;
while ((keyno = tm_it.next_bit()) != key_map::iterator::BITMAP_END)
{
for (order= join->group_list; order; order= order->next)
{
Item *item= order->item[0];
if (item->used_tables() & (table_map(1) << tableno))
{
DBUG_ASSERT(item->real_type() == Item::FIELD_ITEM);
}
}
/*
if (continuation)
{
walk through list and find which key parts are occupied;
// note that the above can't be made any faster.
}
else
use rec_per_key[0];
find out the cardinality.
check if cardinality decreases if we use it;
*/
}
}
}
#endif
/*
Get an estimate of how many records will be produced after the GROUP BY
operation.
@param join Join we're operating on
@param join_op_rows How many records will be produced by the join
operations (this is what join optimizer produces)
@seealso
See also optimize_semijoin_nests(), grep for "Adjust output cardinality
estimates". Very similar code there that is not joined with this one
because we operate on different data structs and too much effort is
needed to abstract them out.
@return
Number of records we expect to get after the GROUP BY operation
*/
double get_post_group_estimate(JOIN* join, double join_op_rows)
{
table_map tables_in_group_list= table_map(0);
/* Find out which tables are used in GROUP BY list */
for (ORDER *order= join->group_list_for_estimates; order; order= order->next)
{
Item *item= order->item[0];
table_map item_used_tables= item->used_tables();
if (item_used_tables & RAND_TABLE_BIT)
{
/* Each join output record will be in its own group */
return join_op_rows;
}
tables_in_group_list|= item_used_tables;
}
tables_in_group_list &= ~PSEUDO_TABLE_BITS;
/*
Use join fanouts to calculate the max. number of records in the group-list
*/
double fanout_rows[MAX_KEY];
bzero(&fanout_rows, sizeof(fanout_rows));
double out_rows;
out_rows= get_fanout_with_deps(join, tables_in_group_list);
#if 0
/* The following will be needed when making use of index stats: */
/*
Also generate max. number of records for each of the tables mentioned
in the group-list. We'll use that a baseline number that we'll try to
reduce by using
- #table-records
- index statistics.
*/
Table_map_iterator tm_it(tables_in_group_list);
int tableno;
while ((tableno = tm_it.next_bit()) != Table_map_iterator::BITMAP_END)
{
fanout_rows[tableno]= get_fanout_with_deps(join, table_map(1) << tableno);
}
/*
Try to bring down estimates using index statistics.
*/
//check_out_index_stats(join);
#endif
return out_rows;
}
/**
Execute a subquery IN predicate via materialization.
@details
If needed materialize the subquery into a temporary table, then
copmpute the predicate via a lookup into this table.
@retval TRUE if error
@retval FALSE otherwise
*/
int subselect_hash_sj_engine::exec()
{
Item_in_subselect *item_in= (Item_in_subselect *) item;
SELECT_LEX *save_select= thd->lex->current_select;
subselect_partial_match_engine *pm_engine= NULL;
int res= 0;
DBUG_ENTER("subselect_hash_sj_engine::exec");
/*
Optimize and materialize the subquery during the first execution of
the subquery predicate.
*/
thd->lex->current_select= materialize_engine->select_lex;
/* The subquery should be optimized, and materialized only once. */
DBUG_ASSERT(materialize_join->optimization_state == JOIN::OPTIMIZATION_DONE &&
!is_materialized);
materialize_join->exec();
if (unlikely((res= MY_TEST(materialize_join->error || thd->is_fatal_error ||
thd->is_error()))))
goto err;
/*
TODO:
- Unlock all subquery tables as we don't need them. To implement this
we need to add new functionality to JOIN::join_free that can unlock
all tables in a subquery (and all its subqueries).
- The temp table used for grouping in the subquery can be freed
immediately after materialization (yet it's done together with
unlocking).
*/
is_materialized= TRUE;
/*
If the subquery returned no rows, the temporary table is empty, so we know
directly that the result of IN is FALSE. We first update the table
statistics, then we test if the temporary table for the query result is
empty.
*/
tmp_table->file->info(HA_STATUS_VARIABLE);
if (!tmp_table->file->stats.records)
{
/* The value of IN will not change during this execution. */
item_in->reset();
item_in->make_const();
item_in->set_first_execution();
thd->lex->current_select= save_select;
DBUG_RETURN(FALSE);
}
/*
TIMOUR: The schema-based analysis for partial matching can be done once for
prepared statement and remembered. It is done here to remove the need to
save/restore all related variables between each re-execution, thus making
the code simpler.
*/
strategy= get_strategy_using_schema();
/* This call may discover that we don't need partial matching at all. */
strategy= get_strategy_using_data();
if (strategy == PARTIAL_MATCH)
{
uint count_pm_keys; /* Total number of keys needed for partial matching. */
MY_BITMAP *nn_key_parts= NULL; /* Key parts of the only non-NULL index. */
uint count_non_null_columns= 0; /* Number of columns in nn_key_parts. */
bool has_covering_null_row;
bool has_covering_null_columns;
select_materialize_with_stats *result_sink=
(select_materialize_with_stats *) result;
uint field_count= tmp_table->s->fields;
if (count_partial_match_columns < field_count)
{
nn_key_parts= &non_null_key_parts;
count_non_null_columns= bitmap_bits_set(nn_key_parts);
}
has_covering_null_row= (result_sink->get_max_nulls_in_row() == field_count);
has_covering_null_columns= (count_non_null_columns +
count_null_only_columns == field_count);
if (has_covering_null_row && has_covering_null_columns)
{
/*
The whole table consist of only NULL values. The result of IN is
a constant UNKNOWN.
*/
DBUG_ASSERT(tmp_table->file->stats.records == 1);
item_in->value= 0;
item_in->null_value= 1;
item_in->make_const();
item_in->set_first_execution();
thd->lex->current_select= save_select;
DBUG_RETURN(FALSE);
}
if (has_covering_null_row)
{
DBUG_ASSERT(count_partial_match_columns == field_count);
count_pm_keys= 0;
}
else if (has_covering_null_columns)
count_pm_keys= 1;
else
count_pm_keys= count_partial_match_columns - count_null_only_columns +
(nn_key_parts ? 1 : 0);
choose_partial_match_strategy(MY_TEST(nn_key_parts),
has_covering_null_row,
&partial_match_key_parts);
DBUG_ASSERT(strategy == PARTIAL_MATCH_MERGE ||
strategy == PARTIAL_MATCH_SCAN);
if (strategy == PARTIAL_MATCH_MERGE)
{
pm_engine=
new subselect_rowid_merge_engine((subselect_uniquesubquery_engine*)
lookup_engine, tmp_table,
count_pm_keys,
has_covering_null_row,
has_covering_null_columns,
count_columns_with_nulls,
item, result,
semi_join_conds->argument_list());
if (!pm_engine ||
pm_engine->prepare(thd) ||
((subselect_rowid_merge_engine*) pm_engine)->
init(nn_key_parts, &partial_match_key_parts))
{
/*
The call to init() would fail if there was not enough memory to allocate
all buffers for the rowid merge strategy. In this case revert to table
scanning which doesn't need any big buffers.
*/
delete pm_engine;
pm_engine= NULL;
strategy= PARTIAL_MATCH_SCAN;
}
}
if (strategy == PARTIAL_MATCH_SCAN)
{
if (!(pm_engine=
new subselect_table_scan_engine((subselect_uniquesubquery_engine*)
lookup_engine, tmp_table,
item, result,
semi_join_conds->argument_list(),
has_covering_null_row,
has_covering_null_columns,
count_columns_with_nulls)) ||
pm_engine->prepare(thd))
{
/* This is an irrecoverable error. */
res= 1;
goto err;
}
}
}
if (pm_engine)
lookup_engine= pm_engine;
item_in->change_engine(lookup_engine);
err:
thd->lex->current_select= save_select;
DBUG_RETURN(res);
}
/**
Print the state of this engine into a string for debugging and views.
*/
void subselect_hash_sj_engine::print(String *str, enum_query_type query_type)
{
str->append(STRING_WITH_LEN(" <materialize> ("));
materialize_engine->print(str, query_type);
str->append(STRING_WITH_LEN(" ), "));
if (lookup_engine)
lookup_engine->print(str, query_type);
else
str->append(STRING_WITH_LEN(
"<engine selected at execution time>"
));
}
bool subselect_hash_sj_engine::fix_length_and_dec(Item_cache** row)
{
DBUG_ASSERT(FALSE);
return FALSE;
}
void subselect_hash_sj_engine::exclude()
{
DBUG_ASSERT(FALSE);
}
bool subselect_hash_sj_engine::no_tables()
{
DBUG_ASSERT(FALSE);
return FALSE;
}
bool subselect_hash_sj_engine::change_result(Item_subselect *si,
select_result_interceptor *res,
bool temp __attribute__((unused)))
{
DBUG_ASSERT(FALSE);
return TRUE;
}
Ordered_key::Ordered_key(uint keyid_arg, TABLE *tbl_arg, Item *search_key_arg,
ha_rows null_count_arg, ha_rows min_null_row_arg,
ha_rows max_null_row_arg, uchar *row_num_to_rowid_arg)
: keyid(keyid_arg), tbl(tbl_arg), search_key(search_key_arg),
row_num_to_rowid(row_num_to_rowid_arg), null_count(null_count_arg)
{
DBUG_ASSERT(tbl->file->stats.records > null_count);
key_buff_elements= tbl->file->stats.records - null_count;
cur_key_idx= HA_POS_ERROR;
DBUG_ASSERT((null_count && min_null_row_arg && max_null_row_arg) ||
(!null_count && !min_null_row_arg && !max_null_row_arg));
if (null_count)
{
/* The counters are 1-based, for key access we need 0-based indexes. */
min_null_row= min_null_row_arg - 1;
max_null_row= max_null_row_arg - 1;
}
else
min_null_row= max_null_row= 0;
}
Ordered_key::~Ordered_key()
{
my_free(key_buff);
my_bitmap_free(&null_key);
}
/*
Cleanup that needs to be done for each PS (re)execution.
*/
void Ordered_key::cleanup()
{
/*
Currently these keys are recreated for each PS re-execution, thus
there is nothing to cleanup, the whole object goes away after execution
is over. All handler related initialization/deinitialization is done by
the parent subselect_rowid_merge_engine object.
*/
}
/*
Initialize a multi-column index.
*/
bool Ordered_key::init(MY_BITMAP *columns_to_index)
{
THD *thd= tbl->in_use;
uint cur_key_col= 0;
Item_field *cur_tmp_field;
Item_func_lt *fn_less_than;
key_column_count= bitmap_bits_set(columns_to_index);
key_columns= (Item_field**) thd->alloc(key_column_count *
sizeof(Item_field*));
compare_pred= (Item_func_lt**) thd->alloc(key_column_count *
sizeof(Item_func_lt*));
if (!key_columns || !compare_pred)
return TRUE; /* Revert to table scan partial match. */
for (uint i= 0; i < columns_to_index->n_bits; i++)
{
if (!bitmap_is_set(columns_to_index, i))
continue;
cur_tmp_field= new (thd->mem_root) Item_field(thd, tbl->field[i]);
/* Create the predicate (tmp_column[i] < outer_ref[i]). */
fn_less_than= new (thd->mem_root) Item_func_lt(thd, cur_tmp_field,
search_key->element_index(i));
fn_less_than->fix_fields(thd, (Item**) &fn_less_than);
key_columns[cur_key_col]= cur_tmp_field;
compare_pred[cur_key_col]= fn_less_than;
++cur_key_col;
}
if (alloc_keys_buffers())
{
/* TIMOUR revert to partial match via table scan. */
return TRUE;
}
return FALSE;
}
/*
Initialize a single-column index.
*/
bool Ordered_key::init(int col_idx)
{
THD *thd= tbl->in_use;
key_column_count= 1;
// TIMOUR: check for mem allocation err, revert to scan
key_columns= (Item_field**) thd->alloc(sizeof(Item_field*));
compare_pred= (Item_func_lt**) thd->alloc(sizeof(Item_func_lt*));
key_columns[0]= new (thd->mem_root) Item_field(thd, tbl->field[col_idx]);
/* Create the predicate (tmp_column[i] < outer_ref[i]). */
compare_pred[0]= new (thd->mem_root) Item_func_lt(thd, key_columns[0],
search_key->element_index(col_idx));
compare_pred[0]->fix_fields(thd, (Item**)&compare_pred[0]);
if (alloc_keys_buffers())
{
/* TIMOUR revert to partial match via table scan. */
return TRUE;
}
return FALSE;
}
/*
Allocate the buffers for both the row number, and the NULL-bitmap indexes.
*/
bool Ordered_key::alloc_keys_buffers()
{
DBUG_ASSERT(key_buff_elements > 0);
if (!(key_buff= (rownum_t*) my_malloc((size_t)(key_buff_elements *
sizeof(rownum_t)), MYF(MY_WME | MY_THREAD_SPECIFIC))))
return TRUE;
/*
TIMOUR: it is enough to create bitmaps with size
(max_null_row - min_null_row), and then use min_null_row as
lookup offset.
*/
/* Notice that max_null_row is max array index, we need count, so +1. */
if (my_bitmap_init(&null_key, NULL, (uint)(max_null_row + 1), FALSE))
return TRUE;
cur_key_idx= HA_POS_ERROR;
return FALSE;
}
/*
Quick sort comparison function that compares two rows of the same table
indentfied with their row numbers.
@retval -1
@retval 0
@retval +1
*/
int
Ordered_key::cmp_keys_by_row_data(ha_rows a, ha_rows b)
{
uchar *rowid_a, *rowid_b;
int __attribute__((unused)) error;
int cmp_res;
/* The length in bytes of the rowids (positions) of tmp_table. */
uint rowid_length= tbl->file->ref_length;
if (a == b)
return 0;
/* Get the corresponding rowids. */
rowid_a= row_num_to_rowid + a * rowid_length;
rowid_b= row_num_to_rowid + b * rowid_length;
/* Fetch the rows for comparison. */
if (unlikely((error= tbl->file->ha_rnd_pos(tbl->record[0], rowid_a))))
{
/* purecov: begin inspected */
tbl->file->print_error(error, MYF(ME_FATALERROR)); // Sets fatal_error
return 0;
/* purecov: end */
}
if (unlikely((error= tbl->file->ha_rnd_pos(tbl->record[1], rowid_b))))
{
/* purecov: begin inspected */
tbl->file->print_error(error, MYF(ME_FATALERROR)); // Sets fatal_error
return 0;
/* purecov: end */
}
/*
Compare the two rows by the corresponding values of the indexed
columns.
*/
for (uint i= 0; i < key_column_count; i++)
{
Field *cur_field= key_columns[i]->field;
if ((cmp_res= cur_field->cmp_offset(tbl->s->rec_buff_length)))
return (cmp_res > 0 ? 1 : -1);
}
return 0;
}
int
Ordered_key::cmp_keys_by_row_data_and_rownum(Ordered_key *key,
rownum_t* a, rownum_t* b)
{
/* The result of comparing the two keys according to their row data. */
int cmp_row_res= key->cmp_keys_by_row_data(*a, *b);
if (cmp_row_res)
return cmp_row_res;
return (*a < *b) ? -1 : (*a > *b) ? 1 : 0;
}
bool Ordered_key::sort_keys()
{
if (tbl->file->ha_rnd_init_with_error(0))
return TRUE;
my_qsort2(key_buff, (size_t) key_buff_elements, sizeof(rownum_t),
(qsort2_cmp) &cmp_keys_by_row_data_and_rownum, (void*) this);
/* Invalidate the current row position. */
cur_key_idx= HA_POS_ERROR;
tbl->file->ha_rnd_end();
return FALSE;
}
/*
The fraction of rows that do not contain NULL in the columns indexed by
this key.
@retval 1 if there are no NULLs
@retval 0 if only NULLs
*/
double Ordered_key::null_selectivity()
{
/* We should not be processing empty tables. */
DBUG_ASSERT(tbl->file->stats.records);
return (1 - (double) null_count / (double) tbl->file->stats.records);
}
/*
Compare the value(s) of the current key in 'search_key' with the
data of the current table record.
@notes The comparison result follows from the way compare_pred
is created in Ordered_key::init. Currently compare_pred compares
a field in of the current row with the corresponding Item that
contains the search key.
@param row_num Number of the row (not index in the key_buff array)
@retval -1 if (current row < search_key)
@retval 0 if (current row == search_key)
@retval +1 if (current row > search_key)
*/
int Ordered_key::cmp_key_with_search_key(rownum_t row_num)
{
/* The length in bytes of the rowids (positions) of tmp_table. */
uint rowid_length= tbl->file->ref_length;
uchar *cur_rowid= row_num_to_rowid + row_num * rowid_length;
int __attribute__((unused)) error;
int cmp_res;
if (unlikely((error= tbl->file->ha_rnd_pos(tbl->record[0], cur_rowid))))
{
/* purecov: begin inspected */
tbl->file->print_error(error, MYF(ME_FATALERROR)); // Sets fatal_error
return 0;
/* purecov: end */
}
for (uint i= 0; i < key_column_count; i++)
{
cmp_res= compare_pred[i]->get_comparator()->compare();
/* Unlike Arg_comparator::compare_row() here there should be no NULLs. */
DBUG_ASSERT(!compare_pred[i]->null_value);
if (cmp_res)
return (cmp_res > 0 ? 1 : -1);
}
return 0;
}
/*
Find a key in a sorted array of keys via binary search.
see create_subq_in_equalities()
*/
bool Ordered_key::lookup()
{
DBUG_ASSERT(key_buff_elements);
ha_rows lo= 0;
ha_rows hi= key_buff_elements - 1;
ha_rows mid;
int cmp_res;
while (lo <= hi)
{
mid= lo + (hi - lo) / 2;
cmp_res= cmp_key_with_search_key(key_buff[mid]);
/*
In order to find the minimum match, check if the pevious element is
equal or smaller than the found one. If equal, we need to search further
to the left.
*/
if (!cmp_res && mid > 0)
cmp_res= !cmp_key_with_search_key(key_buff[mid - 1]) ? 1 : 0;
if (cmp_res == -1)
{
/* row[mid] < search_key */
lo= mid + 1;
}
else if (cmp_res == 1)
{
/* row[mid] > search_key */
if (!mid)
goto not_found;
hi= mid - 1;
}
else
{
/* row[mid] == search_key */
cur_key_idx= mid;
return TRUE;
}
}
not_found:
cur_key_idx= HA_POS_ERROR;
return FALSE;
}
/*
Move the current index pointer to the next key with the same column
values as the current key. Since the index is sorted, all such keys
are contiguous.
*/
bool Ordered_key::next_same()
{
DBUG_ASSERT(key_buff_elements);
if (cur_key_idx < key_buff_elements - 1)
{
/*
TIMOUR:
The below is quite inefficient, since as a result we will fetch every
row (except the last one) twice. There must be a more efficient way,
e.g. swapping record[0] and record[1], and reading only the new record.
*/
if (!cmp_keys_by_row_data(key_buff[cur_key_idx], key_buff[cur_key_idx + 1]))
{
++cur_key_idx;
return TRUE;
}
}
return FALSE;
}
void Ordered_key::print(String *str)
{
uint i;
str->append("{idx=");
str->qs_append(keyid);
str->append(", (");
for (i= 0; i < key_column_count - 1; i++)
{
str->append(&key_columns[i]->field->field_name);
str->append(", ");
}
str->append(&key_columns[i]->field->field_name);
str->append("), ");
str->append("null_bitmap: (bits=");
str->qs_append(null_key.n_bits);
str->append(", nulls= ");
str->qs_append((double)null_count);
str->append(", min_null= ");
str->qs_append((double)min_null_row);
str->append(", max_null= ");
str->qs_append((double)max_null_row);
str->append("), ");
str->append('}');
}
subselect_partial_match_engine::subselect_partial_match_engine(
subselect_uniquesubquery_engine *engine_arg,
TABLE *tmp_table_arg, Item_subselect *item_arg,
select_result_interceptor *result_arg,
List<Item> *equi_join_conds_arg,
bool has_covering_null_row_arg,
bool has_covering_null_columns_arg,
uint count_columns_with_nulls_arg)
:subselect_engine(item_arg, result_arg),
tmp_table(tmp_table_arg), lookup_engine(engine_arg),
equi_join_conds(equi_join_conds_arg),
has_covering_null_row(has_covering_null_row_arg),
has_covering_null_columns(has_covering_null_columns_arg),
count_columns_with_nulls(count_columns_with_nulls_arg)
{}
int subselect_partial_match_engine::exec()
{
Item_in_subselect *item_in= (Item_in_subselect *) item;
int lookup_res;
DBUG_ASSERT(!(item_in->left_expr_has_null() &&
item_in->is_top_level_item()));
if (!item_in->left_expr_has_null())
{
/* Try to find a matching row by index lookup. */
if (lookup_engine->copy_ref_key(false))
{
/* The result is FALSE based on the outer reference. */
item_in->value= 0;
item_in->null_value= 0;
return 0;
}
else
{
/* Search for a complete match. */
if ((lookup_res= lookup_engine->index_lookup()))
{
/* An error occurred during lookup(). */
item_in->value= 0;
item_in->null_value= 0;
return lookup_res;
}
else if (item_in->value || !count_columns_with_nulls)
{
/*
A complete match was found, the result of IN is TRUE.
If no match was found, and there are no NULLs in the materialized
subquery, then the result is guaranteed to be false because this
branch is executed when the outer reference has no NULLs as well.
Notice: (this->item == lookup_engine->item)
*/
return 0;
}
}
}
if (has_covering_null_row)
{
/*
If there is a NULL-only row that covers all columns the result of IN
is UNKNOWN.
*/
item_in->value= 0;
/*
TIMOUR: which one is the right way to propagate an UNKNOWN result?
Should we also set empty_result_set= FALSE; ???
*/
//item_in->was_null= 1;
item_in->null_value= 1;
return 0;
}
/*
There is no complete match. Look for a partial match (UNKNOWN result), or
no match (FALSE).
*/
if (tmp_table->file->inited)
tmp_table->file->ha_index_end();
if (partial_match())
{
/* The result of IN is UNKNOWN. */
item_in->value= 0;
/*
TIMOUR: which one is the right way to propagate an UNKNOWN result?
Should we also set empty_result_set= FALSE; ???
*/
//item_in->was_null= 1;
item_in->null_value= 1;
}
else
{
/* The result of IN is FALSE. */
item_in->value= 0;
/*
TIMOUR: which one is the right way to propagate an UNKNOWN result?
Should we also set empty_result_set= FALSE; ???
*/
//item_in->was_null= 0;
item_in->null_value= 0;
}
return 0;
}
void subselect_partial_match_engine::print(String *str,
enum_query_type query_type)
{
/*
Should never be called as the actual engine cannot be known at query
optimization time.
DBUG_ASSERT(FALSE);
*/
}
/*
@param non_null_key_parts
@param partial_match_key_parts A union of all single-column NULL key parts.
@retval FALSE the engine was initialized successfully
@retval TRUE there was some (memory allocation) error during initialization,
such errors should be interpreted as revert to other strategy
*/
bool
subselect_rowid_merge_engine::init(MY_BITMAP *non_null_key_parts,
MY_BITMAP *partial_match_key_parts)
{
THD *thd= get_thd();
/* The length in bytes of the rowids (positions) of tmp_table. */
uint rowid_length= tmp_table->file->ref_length;
ha_rows row_count= tmp_table->file->stats.records;
rownum_t cur_rownum= 0;
select_materialize_with_stats *result_sink=
(select_materialize_with_stats *) result;
uint cur_keyid= 0;
Item_in_subselect *item_in= (Item_in_subselect*) item;
int error;
if (merge_keys_count == 0)
{
DBUG_ASSERT(bitmap_bits_set(partial_match_key_parts) == 0 ||
has_covering_null_row);
/* There is nothing to initialize, we will only do regular lookups. */
return FALSE;
}
/*
If all nullable columns contain only NULLs, there must be one index
over all non-null columns.
*/
DBUG_ASSERT(!has_covering_null_columns ||
(has_covering_null_columns &&
merge_keys_count == 1 && non_null_key_parts));
/*
Allocate buffers to hold the merged keys and the mapping between rowids and
row numbers. All small buffers are allocated in the runtime memroot. Big
buffers are allocated from the OS via malloc.
*/
if (!(merge_keys= (Ordered_key**) thd->alloc(merge_keys_count *
sizeof(Ordered_key*))) ||
!(null_bitmaps= (MY_BITMAP**) thd->alloc(merge_keys_count *
sizeof(MY_BITMAP*))) ||
!(row_num_to_rowid= (uchar*) my_malloc((size_t)(row_count * rowid_length),
MYF(MY_WME | MY_THREAD_SPECIFIC))))
return TRUE;
/* Create the only non-NULL key if there is any. */
if (non_null_key_parts)
{
non_null_key= new Ordered_key(cur_keyid, tmp_table, item_in->left_expr,
0, 0, 0, row_num_to_rowid);
if (non_null_key->init(non_null_key_parts))
return TRUE;
merge_keys[cur_keyid]= non_null_key;
merge_keys[cur_keyid]->first();
++cur_keyid;
}
/*
If all nullable columns contain NULLs, the only key that is needed is the
only non-NULL key that is already created above.
*/
if (!has_covering_null_columns)
{
if (my_bitmap_init_memroot(&matching_keys, merge_keys_count, thd->mem_root) ||
my_bitmap_init_memroot(&matching_outer_cols, merge_keys_count, thd->mem_root))
return TRUE;
/*
Create one single-column NULL-key for each column in
partial_match_key_parts.
*/
for (uint i= 0; i < partial_match_key_parts->n_bits; i++)
{
/* Skip columns that have no NULLs, or contain only NULLs. */
if (!bitmap_is_set(partial_match_key_parts, i) ||
result_sink->get_null_count_of_col(i) == row_count)
continue;
merge_keys[cur_keyid]= new Ordered_key(
cur_keyid, tmp_table,
item_in->left_expr->element_index(i),
result_sink->get_null_count_of_col(i),
result_sink->get_min_null_of_col(i),
result_sink->get_max_null_of_col(i),
row_num_to_rowid);
if (merge_keys[cur_keyid]->init(i))
return TRUE;
merge_keys[cur_keyid]->first();
++cur_keyid;
}
}
DBUG_ASSERT(cur_keyid == merge_keys_count);
/* Populate the indexes with data from the temporary table. */
if (unlikely(tmp_table->file->ha_rnd_init_with_error(1)))
return TRUE;
tmp_table->file->extra_opt(HA_EXTRA_CACHE,
current_thd->variables.read_buff_size);
tmp_table->null_row= 0;
while (TRUE)
{
error= tmp_table->file->ha_rnd_next(tmp_table->record[0]);
if (error == HA_ERR_ABORTED_BY_USER)
break;
/*
This is a temp table that we fully own, there should be no other
cause to stop the iteration than EOF.
*/
DBUG_ASSERT(!error || error == HA_ERR_END_OF_FILE);
if (unlikely(error == HA_ERR_END_OF_FILE))
{
DBUG_ASSERT(cur_rownum == tmp_table->file->stats.records);
break;
}
/*
Save the position of this record in the row_num -> rowid mapping.
*/
tmp_table->file->position(tmp_table->record[0]);
memcpy(row_num_to_rowid + cur_rownum * rowid_length,
tmp_table->file->ref, rowid_length);
/* Add the current row number to the corresponding keys. */
if (non_null_key)
{
/* By definition there are no NULLs in the non-NULL key. */
non_null_key->add_key(cur_rownum);
}
for (uint i= (non_null_key ? 1 : 0); i < merge_keys_count; i++)
{
/*
Check if the first and only indexed column contains NULL in the current
row, and add the row number to the corresponding key.
*/
if (merge_keys[i]->get_field(0)->is_null())
merge_keys[i]->set_null(cur_rownum);
else
merge_keys[i]->add_key(cur_rownum);
}
++cur_rownum;
}
tmp_table->file->ha_rnd_end();
/* Sort all the keys by their NULL selectivity. */
my_qsort(merge_keys, merge_keys_count, sizeof(Ordered_key*),
(qsort_cmp) cmp_keys_by_null_selectivity);
/* Sort the keys in each of the indexes. */
for (uint i= 0; i < merge_keys_count; i++)
if (merge_keys[i]->sort_keys())
return TRUE;
if (init_queue(&pq, merge_keys_count, 0, FALSE,
subselect_rowid_merge_engine::cmp_keys_by_cur_rownum, NULL,
0, 0))
return TRUE;
return FALSE;
}
subselect_rowid_merge_engine::~subselect_rowid_merge_engine()
{
/* None of the resources below is allocated if there are no ordered keys. */
if (merge_keys_count)
{
my_free(row_num_to_rowid);
for (uint i= 0; i < merge_keys_count; i++)
delete merge_keys[i];
delete_queue(&pq);
if (tmp_table->file->inited == handler::RND)
tmp_table->file->ha_rnd_end();
}
}
void subselect_rowid_merge_engine::cleanup()
{
}
/*
Quick sort comparison function to compare keys in order of decreasing bitmap
selectivity, so that the most selective keys come first.
@param k1 first key to compare
@param k2 second key to compare
@retval 1 if k1 is less selective than k2
@retval 0 if k1 is equally selective as k2
@retval -1 if k1 is more selective than k2
*/
int
subselect_rowid_merge_engine::cmp_keys_by_null_selectivity(Ordered_key **k1,
Ordered_key **k2)
{
double k1_sel= (*k1)->null_selectivity();
double k2_sel= (*k2)->null_selectivity();
if (k1_sel < k2_sel)
return 1;
if (k1_sel > k2_sel)
return -1;
return 0;
}
/*
*/
int
subselect_rowid_merge_engine::cmp_keys_by_cur_rownum(void *arg,
uchar *k1, uchar *k2)
{
rownum_t r1= ((Ordered_key*) k1)->current();
rownum_t r2= ((Ordered_key*) k2)->current();
return (r1 < r2) ? -1 : (r1 > r2) ? 1 : 0;
}
/*
Check if certain table row contains a NULL in all columns for which there is
no match in the corresponding value index.
@note
There is no need to check the columns that contain only NULLs, because
those are guaranteed to match.
@retval TRUE if a NULL row exists
@retval FALSE otherwise
*/
bool subselect_rowid_merge_engine::test_null_row(rownum_t row_num)
{
Ordered_key *cur_key;
for (uint i = 0; i < merge_keys_count; i++)
{
cur_key= merge_keys[i];
if (bitmap_is_set(&matching_keys, cur_key->get_keyid()))
{
/*
The key 'i' (with id 'cur_keyid') already matches a value in row
'row_num', thus we skip it as it can't possibly match a NULL.
*/
continue;
}
if (!cur_key->is_null(row_num))
return FALSE;
}
return TRUE;
}
/**
Test if a subset of NULL-able columns contains a row of NULLs.
@retval TRUE if such a row exists
@retval FALSE no complementing null row
*/
bool subselect_rowid_merge_engine::
exists_complementing_null_row(MY_BITMAP *keys_to_complement)
{
rownum_t highest_min_row= 0;
rownum_t lowest_max_row= UINT_MAX;
uint count_null_keys, i;
Ordered_key *cur_key;
if (!count_columns_with_nulls)
{
/*
If there are both NULLs and non-NUll values in the outer reference, and
the subquery contains no NULLs, a complementing NULL row cannot exist.
*/
return FALSE;
}
for (i= (non_null_key ? 1 : 0), count_null_keys= 0; i < merge_keys_count; i++)
{
cur_key= merge_keys[i];
if (bitmap_is_set(keys_to_complement, cur_key->get_keyid()))
continue;
if (!cur_key->get_null_count())
{
/* If there is column without NULLs, there cannot be a partial match. */
return FALSE;
}
if (cur_key->get_min_null_row() > highest_min_row)
highest_min_row= cur_key->get_min_null_row();
if (cur_key->get_max_null_row() < lowest_max_row)
lowest_max_row= cur_key->get_max_null_row();
null_bitmaps[count_null_keys++]= cur_key->get_null_key();
}
if (lowest_max_row < highest_min_row)
{
/* The intersection of NULL rows is empty. */
return FALSE;
}
return bitmap_exists_intersection((const MY_BITMAP**) null_bitmaps,
count_null_keys,
(uint)highest_min_row, (uint)lowest_max_row);
}
/*
@retval TRUE there is a partial match (UNKNOWN)
@retval FALSE there is no match at all (FALSE)
*/
bool subselect_rowid_merge_engine::partial_match()
{
Ordered_key *min_key; /* Key that contains the current minimum position. */
rownum_t min_row_num; /* Current row number of min_key. */
Ordered_key *cur_key;
rownum_t cur_row_num;
uint count_nulls_in_search_key= 0;
uint max_null_in_any_row=
((select_materialize_with_stats *) result)->get_max_nulls_in_row();
bool res= FALSE;
/* If there is a non-NULL key, it must be the first key in the keys array. */
DBUG_ASSERT(!non_null_key || (non_null_key && merge_keys[0] == non_null_key));
/* The prioryty queue for keys must be empty. */
DBUG_ASSERT(!pq.elements);
/* All data accesses during execution are via handler::ha_rnd_pos() */
if (unlikely(tmp_table->file->ha_rnd_init_with_error(0)))
{
res= FALSE;
goto end;
}
/* Check if there is a match for the columns of the only non-NULL key. */
if (non_null_key && !non_null_key->lookup())
{
res= FALSE;
goto end;
}
/*
If all nullable columns contain only NULLs, then there is a guaranteed
partial match, and we don't need to search for a matching row.
*/
if (has_covering_null_columns)
{
res= TRUE;
goto end;
}
if (non_null_key)
queue_insert(&pq, (uchar *) non_null_key);
/*
Do not add the non_null_key, since it was already processed above.
*/
bitmap_clear_all(&matching_outer_cols);
for (uint i= MY_TEST(non_null_key); i < merge_keys_count; i++)
{
DBUG_ASSERT(merge_keys[i]->get_column_count() == 1);
if (merge_keys[i]->get_search_key(0)->null_value)
{
++count_nulls_in_search_key;
bitmap_set_bit(&matching_outer_cols, merge_keys[i]->get_keyid());
}
else if (merge_keys[i]->lookup())
queue_insert(&pq, (uchar *) merge_keys[i]);
}
/*
If the outer reference consists of only NULLs, or if it has NULLs in all
nullable columns (above we guarantee there is a match for the non-null
coumns), the result is UNKNOWN.
*/
if (count_nulls_in_search_key == merge_keys_count - MY_TEST(non_null_key))
{
res= TRUE;
goto end;
}
/*
If the outer row has NULLs in some columns, and
there is no match for any of the remaining columns, and
there is a subquery row with NULLs in all unmatched columns,
then there is a partial match, otherwise the result is FALSE.
*/
if (count_nulls_in_search_key && !pq.elements)
{
DBUG_ASSERT(!non_null_key);
/*
Check if the intersection of all NULL bitmaps of all keys that
are not in matching_outer_cols is non-empty.
*/
res= exists_complementing_null_row(&matching_outer_cols);
goto end;
}
/*
If there is no NULL (sub)row that covers all NULL columns, and there is no
match for any of the NULL columns, the result is FALSE. Notice that if there
is a non-null key, and there is only one matching key, the non-null key is
the matching key. This is so, because this method returns FALSE if the
non-null key doesn't have a match.
*/
if (!count_nulls_in_search_key &&
(!pq.elements ||
(pq.elements == 1 && non_null_key &&
max_null_in_any_row < merge_keys_count-1)))
{
if (!pq.elements)
{
DBUG_ASSERT(!non_null_key);
/*
The case of a covering null row is handled by
subselect_partial_match_engine::exec()
*/
DBUG_ASSERT(max_null_in_any_row != tmp_table->s->fields);
}
res= FALSE;
goto end;
}
DBUG_ASSERT(pq.elements);
min_key= (Ordered_key*) queue_remove_top(&pq);
min_row_num= min_key->current();
bitmap_set_bit(&matching_keys, min_key->get_keyid());
bitmap_union(&matching_keys, &matching_outer_cols);
if (min_key->next_same())
queue_insert(&pq, (uchar *) min_key);
if (pq.elements == 0)
{
/*
Check the only matching row of the only key min_key for NULL matches
in the other columns.
*/
res= test_null_row(min_row_num);
goto end;
}
while (TRUE)
{
cur_key= (Ordered_key*) queue_remove_top(&pq);
cur_row_num= cur_key->current();
if (cur_row_num == min_row_num)
bitmap_set_bit(&matching_keys, cur_key->get_keyid());
else
{
/* Follows from the correct use of priority queue. */
DBUG_ASSERT(cur_row_num > min_row_num);
if (test_null_row(min_row_num))
{
res= TRUE;
goto end;
}
else
{
min_key= cur_key;
min_row_num= cur_row_num;
bitmap_clear_all(&matching_keys);
bitmap_set_bit(&matching_keys, min_key->get_keyid());
bitmap_union(&matching_keys, &matching_outer_cols);
}
}
if (cur_key->next_same())
queue_insert(&pq, (uchar *) cur_key);
if (pq.elements == 0)
{
/* Check the last row of the last column in PQ for NULL matches. */
res= test_null_row(min_row_num);
goto end;
}
}
/* We should never get here - all branches must be handled explicitly above. */
DBUG_ASSERT(FALSE);
end:
if (!has_covering_null_columns)
bitmap_clear_all(&matching_keys);
queue_remove_all(&pq);
tmp_table->file->ha_rnd_end();
return res;
}
subselect_table_scan_engine::subselect_table_scan_engine(
subselect_uniquesubquery_engine *engine_arg,
TABLE *tmp_table_arg,
Item_subselect *item_arg,
select_result_interceptor *result_arg,
List<Item> *equi_join_conds_arg,
bool has_covering_null_row_arg,
bool has_covering_null_columns_arg,
uint count_columns_with_nulls_arg)
:subselect_partial_match_engine(engine_arg, tmp_table_arg, item_arg,
result_arg, equi_join_conds_arg,
has_covering_null_row_arg,
has_covering_null_columns_arg,
count_columns_with_nulls_arg)
{}
/*
TIMOUR:
This method is based on subselect_uniquesubquery_engine::scan_table().
Consider refactoring somehow, 80% of the code is the same.
for each row_i in tmp_table
{
count_matches= 0;
for each row element row_i[j]
{
if (outer_ref[j] is NULL || row_i[j] is NULL || outer_ref[j] == row_i[j])
++count_matches;
}
if (count_matches == outer_ref.elements)
return TRUE
}
return FALSE
*/
bool subselect_table_scan_engine::partial_match()
{
List_iterator_fast<Item> equality_it(*equi_join_conds);
Item *cur_eq;
uint count_matches;
int error;
bool res;
if (unlikely(tmp_table->file->ha_rnd_init_with_error(1)))
{
res= FALSE;
goto end;
}
tmp_table->file->extra_opt(HA_EXTRA_CACHE,
get_thd()->variables.read_buff_size);
for (;;)
{
error= tmp_table->file->ha_rnd_next(tmp_table->record[0]);
if (unlikely(error))
{
if (error == HA_ERR_END_OF_FILE)
{
error= 0;
break;
}
else
{
error= report_error(tmp_table, error);
break;
}
}
equality_it.rewind();
count_matches= 0;
while ((cur_eq= equality_it++))
{
DBUG_ASSERT(cur_eq->type() == Item::FUNC_ITEM &&
((Item_func*)cur_eq)->functype() == Item_func::EQ_FUNC);
if (!cur_eq->val_int() && !cur_eq->null_value)
break;
++count_matches;
}
if (count_matches == tmp_table->s->fields)
{
res= TRUE; /* Found a matching row. */
goto end;
}
}
res= FALSE;
end:
tmp_table->file->ha_rnd_end();
return res;
}
void subselect_table_scan_engine::cleanup()
{
}
void Item_subselect::register_as_with_rec_ref(With_element *with_elem)
{
with_elem->sq_with_rec_ref.link_in_list(this, &this->next_with_rec_ref);
with_recursive_reference= true;
}
/*
Create an execution tracker for the expression cache we're using for this
subselect; add the tracker to the query plan.
*/
void Item_subselect::init_expr_cache_tracker(THD *thd)
{
if(!expr_cache)
return;
Explain_query *qw= thd->lex->explain;
DBUG_ASSERT(qw);
Explain_node *node= qw->get_node(unit->first_select()->select_number);
if (!node)
return;
DBUG_ASSERT(expr_cache->type() == Item::EXPR_CACHE_ITEM);
node->cache_tracker= ((Item_cache_wrapper *)expr_cache)->init_tracker(qw->mem_root);
}
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