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mariadb/sql/sql_derived.cc
Sergei Petrunia c7fe8e51de Merge 10.11 into 11.0
2023-04-17 16:50:01 +03:00

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/*
Copyright (c) 2002, 2011, 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 */
/*
Derived tables
These were introduced by Sinisa <sinisa@mysql.com>
*/
#include "mariadb.h" /* NO_EMBEDDED_ACCESS_CHECKS */
#include "sql_priv.h"
#include "unireg.h"
#include "sql_select.h"
#include "derived_handler.h"
#include "sql_base.h"
#include "sql_view.h" // check_duplicate_names
#include "sql_acl.h" // SELECT_ACL
#include "sql_class.h"
#include "sql_derived.h"
#include "sql_cte.h"
#include "my_json_writer.h"
#include "opt_trace.h"
typedef bool (*dt_processor)(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_init(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_prepare(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_optimize(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_merge(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_create(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_fill(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_reinit(THD *thd, LEX *lex, TABLE_LIST *derived);
static bool mysql_derived_merge_for_insert(THD *thd, LEX *lex,
TABLE_LIST *derived);
dt_processor processors[]=
{
&mysql_derived_init,
&mysql_derived_prepare,
&mysql_derived_optimize,
&mysql_derived_merge,
&mysql_derived_merge_for_insert,
&mysql_derived_create,
&mysql_derived_fill,
&mysql_derived_reinit,
};
/*
Run specified phases on all derived tables/views in given LEX.
@param lex LEX for this thread
@param phases phases to run derived tables/views through
@return FALSE OK
@return TRUE Error
*/
bool
mysql_handle_derived(LEX *lex, uint phases)
{
bool res= FALSE;
DBUG_ENTER("mysql_handle_derived");
DBUG_PRINT("enter", ("phases: 0x%x", phases));
if (!lex->derived_tables)
DBUG_RETURN(FALSE);
lex->thd->derived_tables_processing= TRUE;
for (uint phase= 0; phase < DT_PHASES && !res; phase++)
{
uint phase_flag= DT_INIT << phase;
if (phase_flag > phases)
break;
if (!(phases & phase_flag))
continue;
for (SELECT_LEX *sl= lex->all_selects_list;
sl && !res;
sl= sl->next_select_in_list())
{
TABLE_LIST *cursor= sl->get_table_list();
sl->changed_elements|= TOUCHED_SEL_DERIVED;
/*
DT_MERGE_FOR_INSERT is not needed for views/derived tables inside
subqueries. Views and derived tables of subqueries should be
processed normally.
*/
if (phases == DT_MERGE_FOR_INSERT &&
cursor && (cursor->top_table()->select_lex !=
lex->first_select_lex()))
continue;
for (;
cursor && !res;
cursor= cursor->next_local)
{
if (!cursor->is_view_or_derived() && phases == DT_MERGE_FOR_INSERT)
continue;
uint8 allowed_phases= (cursor->is_merged_derived() ? DT_PHASES_MERGE :
DT_PHASES_MATERIALIZE | DT_MERGE_FOR_INSERT);
/*
Skip derived tables to which the phase isn't applicable.
TODO: mark derived at the parse time, later set it's type
(merged or materialized)
*/
if ((phase_flag != DT_PREPARE && !(allowed_phases & phase_flag)) ||
(cursor->merged_for_insert && phase_flag != DT_REINIT &&
phase_flag != DT_PREPARE))
continue;
res= (*processors[phase])(lex->thd, lex, cursor);
}
if (lex->describe)
{
/*
Force join->join_tmp creation, because we will use this JOIN
twice for EXPLAIN and we have to have unchanged join for EXPLAINing
*/
sl->uncacheable|= UNCACHEABLE_EXPLAIN;
sl->master_unit()->uncacheable|= UNCACHEABLE_EXPLAIN;
}
}
}
lex->thd->derived_tables_processing= FALSE;
DBUG_RETURN(res);
}
/*
Run through phases for the given derived table/view.
@param lex LEX for this thread
@param derived the derived table to handle
@param phase_map phases to process tables/views through
@details
This function process the derived table (view) 'derived' to performs all
actions that are to be done on the table at the phases specified by
phase_map. The processing is carried out starting from the actions
performed at the earlier phases (those having smaller ordinal numbers).
@note
This function runs specified phases of the derived tables handling on the
given derived table/view. This function is used in the chain of calls:
SELECT_LEX::handle_derived ->
TABLE_LIST::handle_derived ->
mysql_handle_single_derived
This chain of calls implements the bottom-up handling of the derived tables:
i.e. most inner derived tables/views are handled first. This order is
required for the all phases except the merge and the create steps.
For the sake of code simplicity this order is kept for all phases.
@return FALSE ok
@return TRUE error
*/
bool
mysql_handle_single_derived(LEX *lex, TABLE_LIST *derived, uint phases)
{
bool res= FALSE;
uint8 allowed_phases= (derived->is_merged_derived() ? DT_PHASES_MERGE :
DT_PHASES_MATERIALIZE);
DBUG_ENTER("mysql_handle_single_derived");
DBUG_PRINT("enter", ("phases: 0x%x allowed: 0x%x alias: '%s'",
phases, allowed_phases,
(derived->alias.str ? derived->alias.str : "<NULL>")));
if (!lex->derived_tables)
DBUG_RETURN(FALSE);
if (derived->select_lex)
derived->select_lex->changed_elements|= TOUCHED_SEL_DERIVED;
else
DBUG_ASSERT(derived->prelocking_placeholder);
lex->thd->derived_tables_processing= TRUE;
for (uint phase= 0; phase < DT_PHASES; phase++)
{
uint phase_flag= DT_INIT << phase;
if (phase_flag > phases)
break;
if (!(phases & phase_flag))
continue;
/* Skip derived tables to which the phase isn't applicable. */
if (phase_flag != DT_PREPARE &&
!(allowed_phases & phase_flag))
continue;
if ((res= (*processors[phase])(lex->thd, lex, derived)))
break;
}
lex->thd->derived_tables_processing= FALSE;
DBUG_RETURN(res);
}
/**
Merge a derived table/view into the embedding select
@param thd thread handle
@param lex LEX of the embedding query.
@param derived reference to the derived table.
@details
This function merges the given derived table / view into the parent select
construction. Any derived table/reference to view occurred in the FROM
clause of the embedding select is represented by a TABLE_LIST structure a
pointer to which is passed to the function as in the parameter 'derived'.
This structure contains the number/map, alias, a link to SELECT_LEX of the
derived table and other info. If the 'derived' table is used in a nested join
then additionally the structure contains a reference to the ON expression
for this join.
The merge process results in elimination of the derived table (or the
reference to a view) such that:
- the FROM list of the derived table/view is wrapped into a nested join
after which the nest is added to the FROM list of the embedding select
- the WHERE condition of the derived table (view) is ANDed with the ON
condition attached to the table.
@note
Tables are merged into the leaf_tables list, original derived table is removed
from this list also. SELECT_LEX::table_list list is left untouched.
Where expression is merged with derived table's on_expr and can be found after
the merge through the SELECT_LEX::table_list.
Examples of the derived table/view merge:
Schema:
Tables: t1(f1), t2(f2), t3(f3)
View v1: SELECT f1 FROM t1 WHERE f1 < 1
Example with a view:
Before merge:
The query (Q1): SELECT f1,f2 FROM t2 LEFT JOIN v1 ON f1 = f2
(LEX of the main query)
|
(select_lex)
|
(FROM table list)
|
(join list)= t2, v1
/ \
/ (on_expr)= (f1 = f2)
|
(LEX of the v1 view)
|
(select_lex)= SELECT f1 FROM t1 WHERE f1 < 1
After merge:
The rewritten query Q1 (Q1'):
SELECT f1,f2 FROM t2 LEFT JOIN (t1) ON ((f1 = f2) and (f1 < 1))
(LEX of the main query)
|
(select_lex)
|
(FROM table list)
|
(join list)= t2, (t1)
\
(on_expr)= (f1 = f2) and (f1 < 1)
In this example table numbers are assigned as follows:
(outer select): t2 - 1, v1 - 2
(inner select): t1 - 1
After the merge table numbers will be:
(outer select): t2 - 1, t1 - 2
Example with a derived table:
The query Q2:
SELECT f1,f2
FROM (SELECT f1 FROM t1, t3 WHERE f1=f3 and f1 < 1) tt, t2
WHERE f1 = f2
Before merge:
(LEX of the main query)
|
(select_lex)
/ \
(FROM table list) (WHERE clause)= (f1 = f2)
|
(join list)= tt, t2
/ \
/ (on_expr)= (empty)
/
(select_lex)= SELECT f1 FROM t1, t3 WHERE f1 = f3 and f1 < 1
After merge:
The rewritten query Q2 (Q2'):
SELECT f1,f2
FROM (t1, t3) JOIN t2 ON (f1 = f3 and f1 < 1)
WHERE f1 = f2
(LEX of the main query)
|
(select_lex)
/ \
(FROM table list) (WHERE clause)= (f1 = f2)
|
(join list)= t2, (t1, t3)
\
(on_expr)= (f1 = f3 and f1 < 1)
In this example table numbers are assigned as follows:
(outer select): tt - 1, t2 - 2
(inner select): t1 - 1, t3 - 2
After the merge table numbers will be:
(outer select): t1 - 1, t2 - 2, t3 - 3
@return FALSE if derived table/view were successfully merged.
@return TRUE if an error occur.
*/
static
bool mysql_derived_merge(THD *thd, LEX *lex, TABLE_LIST *derived)
{
bool res= FALSE;
SELECT_LEX *dt_select= derived->get_single_select();
table_map map;
uint tablenr;
SELECT_LEX *parent_lex= derived->select_lex;
Query_arena *arena, backup;
DBUG_ENTER("mysql_derived_merge");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
const char *cause= NULL;
if (derived->merged)
{
DBUG_PRINT("info", ("Irreversibly merged: exit"));
DBUG_RETURN(FALSE);
}
if (derived->dt_handler)
{
derived->change_refs_to_fields();
derived->set_materialized_derived();
DBUG_RETURN(FALSE);
}
arena= thd->activate_stmt_arena_if_needed(&backup); // For easier test
if (!derived->merged_for_insert ||
(derived->is_multitable() &&
(thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
thd->lex->sql_command == SQLCOM_DELETE_MULTI)))
{
/*
Check whether there is enough free bits in table map to merge subquery.
If not - materialize it. This check isn't cached so when there is a big
and small subqueries, and the bigger one can't be merged it wouldn't
block the smaller one.
*/
if (parent_lex->get_free_table_map(&map, &tablenr) ||
dt_select->leaf_tables.elements + tablenr > MAX_TABLES)
{
/* There is no enough table bits, fall back to materialization. */
cause= "Not enough table bits to merge subquery";
goto unconditional_materialization;
}
if (dt_select->options & OPTION_SCHEMA_TABLE)
parent_lex->options |= OPTION_SCHEMA_TABLE;
if (!derived->get_unit()->prepared)
{
dt_select->leaf_tables.empty();
make_leaves_list(thd, dt_select->leaf_tables, derived, TRUE, 0);
}
derived->nested_join= (NESTED_JOIN*) thd->calloc(sizeof(NESTED_JOIN));
if (!derived->nested_join)
{
res= TRUE;
goto exit_merge;
}
/* Merge derived table's subquery in the parent select. */
if (parent_lex->merge_subquery(thd, derived, dt_select, tablenr, map))
{
res= TRUE;
goto exit_merge;
}
/*
exclude select lex so it doesn't show up in explain.
do this only for derived table as for views this is already done.
From sql_view.cc
Add subqueries units to SELECT into which we merging current view.
unit(->next)* chain starts with subqueries that are used by this
view and continues with subqueries that are used by other views.
We must not add any subquery twice (otherwise we'll form a loop),
to do this we remember in end_unit the first subquery that has
been already added.
*/
derived->get_unit()->exclude_level();
if (parent_lex->join)
parent_lex->join->table_count+= dt_select->join->table_count - 1;
}
derived->merged= TRUE;
if (derived->get_unit()->prepared)
{
Item *expr= derived->on_expr;
expr= and_conds(thd, expr, dt_select->join ? dt_select->join->conds : 0);
if (expr)
expr->top_level_item();
if (expr && (derived->prep_on_expr || expr != derived->on_expr))
{
derived->on_expr= expr;
derived->prep_on_expr= expr->copy_andor_structure(thd);
}
thd->where= "on clause";
if (derived->on_expr &&
derived->on_expr->fix_fields_if_needed_for_bool(thd, &derived->on_expr))
{
res= TRUE; /* purecov: inspected */
goto exit_merge;
}
// Update used tables cache according to new table map
if (derived->on_expr)
{
derived->on_expr->fix_after_pullout(parent_lex, &derived->on_expr,
TRUE);
fix_list_after_tbl_changes(parent_lex, &derived->nested_join->join_list);
}
}
exit_merge:
if (arena)
thd->restore_active_arena(arena, &backup);
DBUG_RETURN(res);
unconditional_materialization:
if (unlikely(thd->trace_started()))
{
OPT_TRACE_VIEWS_TRANSFORM(thd,trace_wrapper, trace_derived,
derived->is_derived() ? "derived" : "view",
derived->alias.str ? derived->alias.str : "<NULL>",
derived->get_unit()->first_select()->select_number,
"materialized");
trace_derived.add("cause", cause);
}
derived->change_refs_to_fields();
derived->set_materialized_derived();
if (!derived->table || !derived->table->is_created())
res= mysql_derived_create(thd, lex, derived);
goto exit_merge;
}
/**
Merge a view for the embedding INSERT/UPDATE/DELETE
@param thd thread handle
@param lex LEX of the embedding query.
@param derived reference to the derived table.
@details
This function substitutes the derived table for the first table from
the query of the derived table thus making it a correct target table for the
INSERT/UPDATE/DELETE statements. As this operation is correct only for
single table views only, for multi table views this function does nothing.
The derived parameter isn't checked to be a view as derived tables aren't
allowed for INSERT/UPDATE/DELETE statements.
@return FALSE if derived table/view were successfully merged.
@return TRUE if an error occur.
*/
static
bool mysql_derived_merge_for_insert(THD *thd, LEX *lex, TABLE_LIST *derived)
{
DBUG_ENTER("mysql_derived_merge_for_insert");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
DBUG_PRINT("info", ("merged_for_insert: %d is_materialized_derived: %d "
"is_multitable: %d single_table_updatable: %d "
"merge_underlying_list: %d",
derived->merged_for_insert,
derived->is_materialized_derived(),
derived->is_multitable(),
derived->single_table_updatable(),
derived->merge_underlying_list != 0));
if (derived->merged_for_insert)
DBUG_RETURN(FALSE);
if (derived->init_derived(thd, FALSE))
DBUG_RETURN(TRUE);
if (derived->is_materialized_derived())
DBUG_RETURN(mysql_derived_prepare(thd, lex, derived));
if ((thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
thd->lex->sql_command == SQLCOM_DELETE_MULTI))
DBUG_RETURN(FALSE);
if (!derived->is_multitable())
{
if (!derived->single_table_updatable())
DBUG_RETURN(derived->create_field_translation(thd));
if (derived->merge_underlying_list)
{
derived->table= derived->merge_underlying_list->table;
derived->schema_table= derived->merge_underlying_list->schema_table;
derived->merged_for_insert= TRUE;
DBUG_ASSERT(derived->table);
}
}
DBUG_RETURN(FALSE);
}
/*
Initialize a derived table/view
@param thd Thread handle
@param lex LEX of the embedding query.
@param derived reference to the derived table.
@detail
Fill info about derived table/view without preparing an
underlying select. Such as: create a field translation for views, mark it as
a multitable if it is and so on.
@return
false OK
true Error
*/
static
bool mysql_derived_init(THD *thd, LEX *lex, TABLE_LIST *derived)
{
SELECT_LEX_UNIT *unit= derived->get_unit();
DBUG_ENTER("mysql_derived_init");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
// Skip already prepared views/DT
if (!unit || unit->prepared)
DBUG_RETURN(FALSE);
bool res= derived->init_derived(thd, TRUE);
derived->updatable= derived->updatable && derived->is_view();
DBUG_RETURN(res);
}
/**
@brief
Prevent name resolution out of context of ON expressions in derived tables
@param
join_list list of tables used in from list of a derived
@details
The function sets the Name_resolution_context::outer_context to NULL
for all ON expressions contexts in the given join list. It does this
recursively for all nested joins the list contains.
*/
static void nullify_outer_context_for_on_clauses(List<TABLE_LIST>& join_list)
{
List_iterator<TABLE_LIST> li(join_list);
while (TABLE_LIST *table= li++)
{
if (table->on_context)
table->on_context->outer_context= NULL;
if (table->nested_join)
nullify_outer_context_for_on_clauses(table->nested_join->join_list);
}
}
/*
Create temporary table structure (but do not fill it)
@param thd Thread handle
@param lex LEX of the embedding query.
@param derived reference to the derived table.
@detail
Prepare underlying select for a derived table/view. To properly resolve
names in the embedding query the TABLE structure is created. Actual table
is created later by the mysql_derived_create function.
This function is called before any command containing derived table
is executed. All types of derived tables are handled by this function:
- Anonymous derived tables, or
- Named derived tables (aka views).
The table reference, contained in @c derived, is updated with the
fields of a new temporary table.
Derived tables are stored in @c thd->derived_tables and closed by
close_thread_tables().
This function is part of the procedure that starts in
open_and_lock_tables(), a procedure that - among other things - introduces
new table and table reference objects (to represent derived tables) that
don't exist in the privilege database. This means that normal privilege
checking cannot handle them. Hence this function does some extra tricks in
order to bypass normal privilege checking, by exploiting the fact that the
current state of privilege verification is attached as GRANT_INFO structures
on the relevant TABLE and TABLE_REF objects.
For table references, the current state of accrued access is stored inside
TABLE_LIST::grant. Hence this function must update the state of fulfilled
privileges for the new TABLE_LIST, an operation which is normally performed
exclusively by the table and database access checking functions,
check_access() and check_grant(), respectively. This modification is done
for both views and anonymous derived tables: The @c SELECT privilege is set
as fulfilled by the user. However, if a view is referenced and the table
reference is queried against directly (see TABLE_LIST::referencing_view),
the state of privilege checking (GRANT_INFO struct) is copied as-is to the
temporary table.
Only the TABLE structure is created here, actual table is created by the
mysql_derived_create function.
@note This function sets @c SELECT_ACL for @c TEMPTABLE views as well as
anonymous derived tables, but this is ok since later access checking will
distinguish between them.
@see mysql_handle_derived(), mysql_derived_fill(), GRANT_INFO
@return
false OK
true Error
*/
static
bool mysql_derived_prepare(THD *thd, LEX *lex, TABLE_LIST *derived)
{
SELECT_LEX_UNIT *unit= derived->get_unit();
SELECT_LEX *first_select;
bool res= FALSE, keep_row_order, distinct;
DBUG_ENTER("mysql_derived_prepare");
DBUG_PRINT("enter", ("unit: %p table_list: %p alias: '%s'",
unit, derived, derived->alias.str));
if (!unit)
DBUG_RETURN(FALSE);
first_select= unit->first_select();
/*
If rownum() is used we have to preserve the insert row order
to make GROUP BY and ORDER BY with filesort work.
SELECT * from (SELECT a,b from t1 ORDER BY a)) WHERE rownum <= 0;
When rownum is not used the optimizer will skip the ORDER BY clause.
With rownum we have to keep the ORDER BY as this is what is expected.
We also have to create any sort result temporary table in such a way
that the inserted row order is maintained.
*/
keep_row_order= (thd->lex->with_rownum &&
(first_select->group_list.elements ||
first_select->order_list.elements));
if (derived->is_recursive_with_table() &&
!derived->is_with_table_recursive_reference() &&
!derived->with->rec_result && derived->with->get_sq_rec_ref())
{
/*
This is a non-recursive reference to a recursive CTE whose
specification unit has not been prepared at the regular processing of
derived table references. This can happen only in the case when
the specification unit has no recursive references at the top level.
Force the preparation of the specification unit. Use a recursive
table reference from a subquery for this.
*/
DBUG_ASSERT(derived->with->get_sq_rec_ref());
if (unlikely(mysql_derived_prepare(lex->thd, lex,
derived->with->get_sq_rec_ref())))
DBUG_RETURN(TRUE);
}
if (unit->prepared && derived->is_recursive_with_table() &&
!derived->table)
{
/*
Here 'derived' is either a non-recursive table reference to a recursive
with table or a recursive table reference to a recursvive table whose
specification has been already prepared (a secondary recursive table
reference.
*/
if (!(derived->derived_result= new (thd->mem_root) select_unit(thd)))
DBUG_RETURN(TRUE); // out of memory
thd->create_tmp_table_for_derived= TRUE;
res= derived->derived_result->create_result_table(
thd, &unit->types, FALSE,
(first_select->options |
thd->variables.option_bits |
TMP_TABLE_ALL_COLUMNS),
&derived->alias, FALSE, FALSE,
keep_row_order, 0);
thd->create_tmp_table_for_derived= FALSE;
if (likely(!res) && !derived->table)
{
derived->derived_result->set_unit(unit);
derived->table= derived->derived_result->table;
if (derived->is_with_table_recursive_reference())
{
/* Here 'derived" is a secondary recursive table reference */
unit->with_element->rec_result->rec_table_refs.push_back(derived);
}
}
DBUG_ASSERT(derived->table || res);
goto exit;
}
// Skip already prepared views/DT
if (unit->prepared ||
(derived->merged_for_insert &&
!(derived->is_multitable() &&
(thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
thd->lex->sql_command == SQLCOM_DELETE_MULTI))))
{
/*
System versioned tables may still require to get versioning conditions
when modifying view (see vers_setup_conds()). Only UPDATE and DELETE are
affected because they use WHERE condition.
*/
if (!unit->prepared &&
derived->table->versioned() &&
derived->merge_underlying_list &&
/* choose only those merged views that do not select from other views */
!derived->merge_underlying_list->merge_underlying_list)
{
switch (thd->lex->sql_command)
{
case SQLCOM_DELETE:
case SQLCOM_DELETE_MULTI:
case SQLCOM_UPDATE:
case SQLCOM_UPDATE_MULTI:
if ((res= first_select->vers_setup_conds(thd,
derived->merge_underlying_list)))
goto exit;
if (derived->merge_underlying_list->where)
{
Query_arena_stmt on_stmt_arena(thd);
derived->where= and_items(thd, derived->where,
derived->merge_underlying_list->where);
}
default:
break;
}
}
DBUG_RETURN(FALSE);
}
/* prevent name resolving out of derived table */
for (SELECT_LEX *sl= first_select; sl; sl= sl->next_select())
{
// Prevent it for the WHERE clause
sl->context.outer_context= 0;
// And for ON clauses, if there are any
nullify_outer_context_for_on_clauses(*sl->join_list);
if (!derived->is_with_table_recursive_reference() ||
(!derived->with->with_anchor &&
!derived->with->is_with_prepared_anchor()))
{
/*
Prepare underlying views/DT first unless 'derived' is a recursive
table reference and either the anchors from the specification of
'derived' has been already prepared or there no anchor in this
specification
*/
if ((res= sl->handle_derived(lex, DT_PREPARE)))
goto exit;
}
if (derived->outer_join && sl->first_cond_optimization)
{
/* Mark that table is part of OUTER JOIN and fields may be NULL */
for (TABLE_LIST *cursor= (TABLE_LIST*) sl->table_list.first;
cursor;
cursor= cursor->next_local)
cursor->outer_join|= JOIN_TYPE_OUTER;
}
}
if (unlikely(thd->trace_started()))
{
/*
Add to optimizer trace whether a derived table/view
is merged into the parent select or not.
*/
OPT_TRACE_VIEWS_TRANSFORM(thd, trace_wrapper, trace_derived,
derived->is_derived() ? "derived" : "view",
derived->alias.str ? derived->alias.str : "<NULL>",
derived->get_unit()->first_select()->select_number,
derived->is_merged_derived() ? "merged" : "materialized");
}
/*
Above cascade call of prepare is important for PS protocol, but after it
is called we can check if we really need prepare for this derived
*/
if (derived->merged)
{
DBUG_PRINT("info", ("Irreversibly merged: exit"));
DBUG_RETURN(FALSE);
}
derived->fill_me= FALSE;
if ((!derived->is_with_table_recursive_reference() ||
!derived->derived_result) &&
!(derived->derived_result= new (thd->mem_root) select_unit(thd)))
DBUG_RETURN(TRUE); // out of memory
// st_select_lex_unit::prepare correctly work for single select
if ((res= unit->prepare(derived, derived->derived_result, 0)))
goto exit;
if (derived->with &&
(res= derived->with->process_columns_of_derived_unit(thd, unit)))
goto exit;
if ((res= check_duplicate_names(thd, unit->types, 0)))
goto exit;
/*
Check whether we can merge this derived table into main select.
Depending on the result field translation will or will not
be created.
*/
if (!derived->is_with_table_recursive_reference() &&
derived->init_derived(thd, FALSE))
goto exit;
/*
Temp table is created so that it honors if UNION without ALL is to be
processed
We pass as 'distinct' parameter in any of the above cases
1) It is an UNION and the last part of an union is distinct (as
thus the final temporary table should not contain duplicates).
2) It is not an UNION and the unit->distinct flag is set. This is the
case for WHERE A IN (...).
Note that the underlying query will also control distinct condition.
*/
thd->create_tmp_table_for_derived= TRUE;
distinct= (unit->first_select()->next_select() ?
unit->union_distinct && !unit->union_distinct->next_select() :
unit->distinct);
if (!(derived->table) &&
derived->derived_result->create_result_table(thd, &unit->types,
distinct,
(first_select->options |
thd->variables.option_bits |
TMP_TABLE_ALL_COLUMNS),
&derived->alias,
FALSE, FALSE, keep_row_order,
0))
{
thd->create_tmp_table_for_derived= FALSE;
goto exit;
}
thd->create_tmp_table_for_derived= FALSE;
if (!derived->table)
derived->table= derived->derived_result->table;
DBUG_ASSERT(derived->table);
if (derived->is_derived() && derived->is_merged_derived())
first_select->mark_as_belong_to_derived(derived);
derived->dt_handler= derived->find_derived_handler(thd);
if (derived->dt_handler)
{
char query_buff[4096];
String derived_query(query_buff, sizeof(query_buff), thd->charset());
derived_query.length(0);
derived->derived->print(&derived_query,
enum_query_type(QT_VIEW_INTERNAL |
QT_ITEM_ORIGINAL_FUNC_NULLIF |
QT_PARSABLE));
if (!thd->make_lex_string(&derived->derived_spec,
derived_query.ptr(), derived_query.length()))
{
delete derived->dt_handler;
derived->dt_handler= NULL;
}
}
exit:
/* Hide "Unknown column" or "Unknown function" error */
if (derived->view)
{
if (thd->is_error() &&
(thd->get_stmt_da()->sql_errno() == ER_BAD_FIELD_ERROR ||
thd->get_stmt_da()->sql_errno() == ER_FUNC_INEXISTENT_NAME_COLLISION ||
thd->get_stmt_da()->sql_errno() == ER_SP_DOES_NOT_EXIST))
{
thd->clear_error();
my_error(ER_VIEW_INVALID, MYF(0), derived->db.str,
derived->table_name.str);
}
}
/*
if it is preparation PS only or commands that need only VIEW structure
then we do not need real data and we can skip execution (and parameters
is not defined, too)
*/
if (res)
{
if (!derived->is_with_table_recursive_reference())
{
if (derived->table && derived->table->s->tmp_table)
free_tmp_table(thd, derived->table);
delete derived->derived_result;
}
}
else
{
TABLE *table= derived->table;
table->derived_select_number= first_select->select_number;
table->s->tmp_table= INTERNAL_TMP_TABLE;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
if (derived->is_view())
table->grant= derived->grant;
else
{
DBUG_ASSERT(derived->is_derived());
DBUG_ASSERT(derived->is_anonymous_derived_table());
table->grant.privilege= SELECT_ACL;
derived->grant.privilege= SELECT_ACL;
}
#endif
/* Add new temporary table to list of open derived tables */
if (!derived->is_with_table_recursive_reference())
{
table->next= thd->derived_tables;
thd->derived_tables= table;
}
/* If table is used by a left join, mark that any column may be null */
if (derived->outer_join)
table->maybe_null= 1;
}
DBUG_RETURN(res);
}
/**
Runs optimize phase for a derived table/view.
@param thd thread handle
@param lex LEX of the embedding query.
@param derived reference to the derived table.
@details
Runs optimize phase for given 'derived' derived table/view.
If optimizer finds out that it's of the type "SELECT a_constant" then this
functions also materializes it.
@return FALSE ok.
@return TRUE if an error occur.
*/
static
bool mysql_derived_optimize(THD *thd, LEX *lex, TABLE_LIST *derived)
{
SELECT_LEX_UNIT *unit= derived->get_unit();
SELECT_LEX *first_select= unit->first_select();
SELECT_LEX *save_current_select= lex->current_select;
bool res= FALSE;
DBUG_ENTER("mysql_derived_optimize");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
if (derived->merged)
{
DBUG_PRINT("info", ("Irreversibly merged: exit"));
DBUG_RETURN(FALSE);
}
if (derived->is_materialized_derived() && derived->dt_handler)
{
/* Create an object for execution of the query specifying the table */
if (!(derived->pushdown_derived=
new (thd->mem_root) Pushdown_derived(derived, derived->dt_handler)))
DBUG_RETURN(TRUE);
}
lex->current_select= first_select;
if (unit->is_unit_op())
{
if (unit->optimized)
DBUG_RETURN(FALSE);
// optimize union without execution
res= unit->optimize();
}
else if (unit->derived)
{
if (!derived->is_merged_derived())
{
JOIN *join= first_select->join;
unit->set_limit(unit->global_parameters());
if (join &&
join->optimization_state == JOIN::OPTIMIZATION_PHASE_1_DONE &&
join->with_two_phase_optimization)
{
if (unit->optimized_2)
DBUG_RETURN(FALSE);
unit->optimized_2= TRUE;
}
else
{
if (unit->optimized)
DBUG_RETURN(FALSE);
unit->optimized= TRUE;
if (!join)
{
/*
This happens when derived is used in SELECT for which
zer_result_cause != 0.
In this case join is already destroyed.
*/
DBUG_RETURN(FALSE);
}
}
if ((res= join->optimize()))
goto err;
if (join->table_count == join->const_tables)
derived->fill_me= TRUE;
}
}
/*
Materialize derived tables/views of the "SELECT a_constant" type.
Such tables should be materialized at the optimization phase for
correct constant evaluation.
*/
if (!res && derived->fill_me && !derived->merged_for_insert)
{
if (derived->is_merged_derived())
{
derived->change_refs_to_fields();
derived->set_materialized_derived();
}
if ((res= mysql_derived_create(thd, lex, derived)))
goto err;
if ((res= mysql_derived_fill(thd, lex, derived)))
goto err;
}
err:
lex->current_select= save_current_select;
DBUG_RETURN(res);
}
/**
Actually create result table for a materialized derived table/view.
@param thd thread handle
@param lex LEX of the embedding query.
@param derived reference to the derived table.
@details
This function actually creates the result table for given 'derived'
table/view, but it doesn't fill it.
'thd' and 'lex' parameters are not used by this function.
@return FALSE ok.
@return TRUE if an error occur.
*/
static
bool mysql_derived_create(THD *thd, LEX *lex, TABLE_LIST *derived)
{
DBUG_ENTER("mysql_derived_create");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
TABLE *table= derived->table;
SELECT_LEX_UNIT *unit= derived->get_unit();
if (table->is_created())
DBUG_RETURN(FALSE);
select_unit *result= derived->derived_result;
if (table->s->db_type() == TMP_ENGINE_HTON)
{
result->tmp_table_param.keyinfo= table->s->key_info;
if (create_internal_tmp_table(table, result->tmp_table_param.keyinfo,
result->tmp_table_param.start_recinfo,
&result->tmp_table_param.recinfo,
(unit->first_select()->options |
thd->variables.option_bits | TMP_TABLE_ALL_COLUMNS)))
DBUG_RETURN(TRUE);
}
if (open_tmp_table(table))
DBUG_RETURN(TRUE);
table->file->extra(HA_EXTRA_WRITE_CACHE);
table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
DBUG_RETURN(FALSE);
}
void TABLE_LIST::register_as_derived_with_rec_ref(With_element *rec_elem)
{
rec_elem->derived_with_rec_ref.link_in_list(this, &this->next_with_rec_ref);
is_derived_with_recursive_reference= true;
get_unit()->uncacheable|= UNCACHEABLE_DEPENDENT;
}
bool TABLE_LIST::is_nonrecursive_derived_with_rec_ref()
{
return is_derived_with_recursive_reference;
}
/**
@brief
Fill the recursive with table
@param thd The thread handle
@details
The method is called only for recursive with tables.
The method executes the recursive part of the specification
of this with table until no more rows are added to the table
or the number of the performed iteration reaches the allowed
maximum.
@retval
false on success
true on failure
*/
bool TABLE_LIST::fill_recursive(THD *thd)
{
bool rc= false;
st_select_lex_unit *unit= get_unit();
rc= with->instantiate_tmp_tables();
while (!rc && !with->all_are_stabilized())
{
if (with->level > thd->variables.max_recursive_iterations)
break;
with->prepare_for_next_iteration();
rc= unit->exec_recursive();
}
if (!rc)
{
TABLE *src= with->rec_result->table;
rc =src->insert_all_rows_into_tmp_table(thd,
table,
&with->rec_result->tmp_table_param,
true);
}
return rc;
}
/*
Execute subquery of a materialized derived table/view and fill the result
table.
@param thd Thread handle
@param lex LEX for this thread
@param derived reference to the derived table.
@details
Execute subquery of given 'derived' table/view and fill the result
table. After result table is filled, if this is not the EXPLAIN statement
and the table is not specified with a recursion the entire unit / node
is deleted. unit is deleted if UNION is used for derived table and node
is deleted is it is a simple SELECT.
'lex' is unused and 'thd' is passed as an argument to an underlying function.
@note
If you use this function, make sure it's not called at prepare.
Due to evaluation of LIMIT clause it can not be used at prepared stage.
@return FALSE OK
@return TRUE Error
*/
static
bool mysql_derived_fill(THD *thd, LEX *lex, TABLE_LIST *derived)
{
Field_iterator_table field_iterator;
SELECT_LEX_UNIT *unit= derived->get_unit();
bool derived_is_recursive= derived->is_recursive_with_table();
bool res= FALSE;
DBUG_ENTER("mysql_derived_fill");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
if (unit->executed && !unit->uncacheable && !unit->describe &&
!derived_is_recursive)
DBUG_RETURN(FALSE);
/*check that table creation passed without problems. */
DBUG_ASSERT(derived->table && derived->table->is_created());
select_unit *derived_result= derived->derived_result;
SELECT_LEX *save_current_select= lex->current_select;
if (derived->pushdown_derived)
{
int res;
if (unit->executed)
DBUG_RETURN(FALSE);
/* Execute the query that specifies the derived table by a foreign engine */
res= derived->pushdown_derived->execute();
unit->executed= true;
DBUG_RETURN(res);
}
if (unit->executed && !derived_is_recursive &&
(unit->uncacheable & UNCACHEABLE_DEPENDENT))
{
if ((res= derived->table->file->ha_delete_all_rows()))
goto err;
JOIN *join= unit->first_select()->join;
join->first_record= false;
for (uint i= join->top_join_tab_count;
i < join->top_join_tab_count + join->aggr_tables;
i++)
{
if ((res= join->join_tab[i].table->file->ha_delete_all_rows()))
goto err;
}
}
if (derived_is_recursive)
{
if (derived->is_with_table_recursive_reference())
{
/* Here only one iteration step is performed */
res= unit->exec_recursive();
}
else
{
/* In this case all iteration are performed */
res= derived->fill_recursive(thd);
}
}
else if (unit->is_unit_op())
{
// execute union without clean up
res= unit->exec();
}
else
{
SELECT_LEX *first_select= unit->first_select();
unit->set_limit(unit->global_parameters());
if (unit->lim.is_unlimited())
first_select->options&= ~OPTION_FOUND_ROWS;
lex->current_select= first_select;
res= mysql_select(thd,
first_select->table_list.first,
first_select->item_list, first_select->where,
(first_select->order_list.elements+
first_select->group_list.elements),
first_select->order_list.first,
first_select->group_list.first,
first_select->having, (ORDER*) NULL,
(first_select->options |thd->variables.option_bits |
SELECT_NO_UNLOCK),
derived_result, unit, first_select);
}
if (!res && !derived_is_recursive)
{
if (derived_result->flush())
res= TRUE;
unit->executed= TRUE;
if (derived->field_translation)
{
/* reset translation table to materialized table */
field_iterator.set_table(derived->table);
for (uint i= 0;
!field_iterator.end_of_fields();
field_iterator.next(), i= i + 1)
{
Item *item;
if (!(item= field_iterator.create_item(thd)))
{
res= TRUE;
break;
}
thd->change_item_tree(&derived->field_translation[i].item, item);
}
}
}
err:
if (res || (!derived_is_recursive && !lex->describe && !unit->uncacheable))
unit->cleanup();
lex->current_select= save_current_select;
DBUG_RETURN(res);
}
/**
Re-initialize given derived table/view for the next execution.
@param thd thread handle
@param lex LEX for this thread
@param derived reference to the derived table.
@details
Re-initialize given 'derived' table/view for the next execution.
All underlying views/derived tables are recursively reinitialized prior
to re-initialization of given derived table.
'thd' and 'lex' are passed as arguments to called functions.
@return FALSE OK
@return TRUE Error
*/
static
bool mysql_derived_reinit(THD *thd, LEX *lex, TABLE_LIST *derived)
{
DBUG_ENTER("mysql_derived_reinit");
DBUG_PRINT("enter", ("Alias: '%s' Unit: %p",
(derived->alias.str ? derived->alias.str : "<NULL>"),
derived->get_unit()));
st_select_lex_unit *unit= derived->get_unit();
derived->merged_for_insert= FALSE;
unit->unclean();
unit->types.empty();
/* for derived tables & PS (which can't be reset by Item_subselect) */
unit->reinit_exec_mechanism();
unit->set_thd(thd);
DBUG_RETURN(FALSE);
}
/*
@brief
Given condition cond and transformer+argument, try transforming as many
conjuncts as possible.
@detail
The motivation of this function is to convert the condition that's being
pushed into a WHERE clause with derived_field_transformer_for_where or
with derived_grouping_field_transformer_for_where.
The transformer may fail for some sub-condition, in this case we want to
convert the most restrictive part of the condition that can be pushed.
This function only does it for top-level AND: conjuncts that could not be
converted are dropped.
@return
Converted condition, or NULL if nothing could be converted
*/
Item *transform_condition_or_part(THD *thd,
Item *cond,
Item_transformer transformer,
uchar *arg)
{
if (cond->type() != Item::COND_ITEM ||
((Item_cond*) cond)->functype() != Item_func::COND_AND_FUNC)
{
Item *new_item= cond->transform(thd, transformer, arg);
// Indicate that the condition is not pushable
if (!new_item)
cond->clear_extraction_flag();
return new_item;
}
List_iterator<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item=li++))
{
Item *new_item= item->transform(thd, transformer, arg);
if (!new_item)
{
// Indicate that the condition is not pushable
item->clear_extraction_flag();
li.remove();
}
else
li.replace(new_item);
}
switch (((Item_cond*) cond)->argument_list()->elements)
{
case 0:
return NULL;
case 1:
return ((Item_cond*) cond)->argument_list()->head();
default:
return cond;
}
}
/**
@brief
Extract condition that can be pushed into a derived table/view
@param thd the thread handle
@param cond current condition
@param derived the reference to the derived table/view
@details
This function builds the most restrictive condition depending only on
the derived table/view (directly or indirectly through equality) that
can be extracted from the given condition cond and pushes it into the
derived table/view.
Example of the transformation:
SELECT *
FROM t1,
(
SELECT x,MAX(y) AS max_y
FROM t2
GROUP BY x
) AS d_tab
WHERE d_tab.x>1 AND d_tab.max_y<30;
=>
SELECT *
FROM t1,
(
SELECT x,z,MAX(y) AS max_y
FROM t2
WHERE x>1
HAVING max_y<30
GROUP BY x
) AS d_tab
WHERE d_tab.x>1 AND d_tab.max_y<30;
In details:
1. Check what pushable formula can be extracted from cond
2. Build a clone PC of the formula that can be extracted
(the clone is built only if the extracted formula is a AND subformula
of cond or conjunction of such subformulas)
Do for every select specifying derived table/view:
3. If there is no HAVING clause prepare PC to be conjuncted with
WHERE clause of the select. Otherwise do 4-7.
4. Check what formula PC_where can be extracted from PC to be pushed
into the WHERE clause of the select
5. Build PC_where and if PC_where is a conjunct(s) of PC remove it from PC
getting PC_having
6. Prepare PC_where to be conjuncted with the WHERE clause of the select
7. Prepare PC_having to be conjuncted with the HAVING clause of the select
@note
This method is similar to pushdown_cond_for_in_subquery()
@retval TRUE if an error occurs
@retval FALSE otherwise
*/
bool pushdown_cond_for_derived(THD *thd, Item *cond, TABLE_LIST *derived)
{
DBUG_ENTER("pushdown_cond_for_derived");
if (!cond)
DBUG_RETURN(false);
st_select_lex_unit *unit= derived->get_unit();
st_select_lex *first_sl= unit->first_select();
st_select_lex *sl= first_sl;
if (derived->prohibit_cond_pushdown)
DBUG_RETURN(false);
/* Do not push conditions into constant derived */
if (unit->executed)
DBUG_RETURN(false);
/* Do not push conditions into recursive with tables */
if (derived->is_recursive_with_table())
DBUG_RETURN(false);
/* Do not push conditions into unit with global ORDER BY ... LIMIT */
if (unit->fake_select_lex &&
unit->fake_select_lex->limit_params.explicit_limit)
DBUG_RETURN(false);
/* Check whether any select of 'unit' allows condition pushdown */
bool some_select_allows_cond_pushdown= false;
for (; sl; sl= sl->next_select())
{
if (sl->cond_pushdown_is_allowed())
{
some_select_allows_cond_pushdown= true;
break;
}
}
if (!some_select_allows_cond_pushdown)
DBUG_RETURN(false);
/* 1. Check what pushable formula can be extracted from cond */
Item *extracted_cond;
cond->check_pushable_cond(&Item::pushable_cond_checker_for_derived,
(uchar *)(&derived->table->map));
/* 2. Build a clone PC of the formula that can be extracted */
extracted_cond=
cond->build_pushable_cond(thd,
&Item::pushable_equality_checker_for_derived,
((uchar *)&derived->table->map));
if (!extracted_cond)
{
/* Nothing can be pushed into the derived table */
DBUG_RETURN(false);
}
st_select_lex *save_curr_select= thd->lex->current_select;
for (; sl; sl= sl->next_select())
{
Item *extracted_cond_copy;
if (!sl->cond_pushdown_is_allowed())
continue;
/*
For each select of the unit except the last one
create a clone of extracted_cond
*/
extracted_cond_copy= !sl->next_select() ?
extracted_cond :
extracted_cond->build_clone(thd);
if (!extracted_cond_copy)
continue;
/*
Rename the columns of all non-first selects of a union to be compatible
by names with the columns of the first select. It will allow to use copies
of the same expression pushed into having clauses of different selects.
*/
if (sl != first_sl)
{
DBUG_ASSERT(sl->item_list.elements == first_sl->item_list.elements);
List_iterator_fast<Item> it(sl->item_list);
List_iterator_fast<Item> nm_it(unit->types);
while (Item *item= it++)
item->share_name_with(nm_it++);
}
/* Collect fields that are used in the GROUP BY of sl */
if (sl->have_window_funcs())
{
if (sl->group_list.first || sl->join->implicit_grouping)
continue;
ORDER *common_partition_fields=
sl->find_common_window_func_partition_fields(thd);
if (!common_partition_fields)
continue;
sl->collect_grouping_fields_for_derived(thd, common_partition_fields);
}
else
sl->collect_grouping_fields_for_derived(thd, sl->group_list.first);
Item *remaining_cond= NULL;
/* Do 4-6 */
sl->pushdown_cond_into_where_clause(thd, extracted_cond_copy,
&remaining_cond,
&Item::derived_field_transformer_for_where,
(uchar *) sl);
if (!remaining_cond)
continue;
/*
7. Prepare PC_having to be conjuncted with the HAVING clause of
the select
*/
remaining_cond=
remaining_cond->transform(thd,
&Item::derived_field_transformer_for_having,
(uchar *) sl);
if (!remaining_cond)
continue;
if (remaining_cond->walk(&Item::cleanup_excluding_const_fields_processor,
0, 0))
continue;
mark_or_conds_to_avoid_pushdown(remaining_cond);
sl->cond_pushed_into_having= remaining_cond;
}
thd->lex->current_select= save_curr_select;
DBUG_RETURN(false);
}
/**
@brief
Look for provision of the derived_handler interface by a foreign engine
@param thd The thread handler
@details
The function looks through its tables of the query that specifies this
derived table searching for a table whose handlerton owns a
create_derived call-back function. If the call of this function returns
a derived_handler interface object then the server will push the query
specifying the derived table into this engine.
This is a responsibility of the create_derived call-back function to
check whether the engine can execute the query.
@retval the found derived_handler if the search is successful
0 otherwise
*/
derived_handler *TABLE_LIST::find_derived_handler(THD *thd)
{
if (!derived || is_recursive_with_table())
return 0;
for (SELECT_LEX *sl= derived->first_select(); sl; sl= sl->next_select())
{
if (!(sl->join))
continue;
for (TABLE_LIST *tbl= sl->join->tables_list; tbl; tbl= tbl->next_local)
{
if (!tbl->table)
continue;
handlerton *ht= tbl->table->file->partition_ht();
if (!ht->create_derived)
continue;
derived_handler *dh= ht->create_derived(thd, this);
if (dh)
{
dh->set_derived(this);
return dh;
}
}
}
return 0;
}
TABLE_LIST *TABLE_LIST::get_first_table()
{
for (SELECT_LEX *sl= derived->first_select(); sl; sl= sl->next_select())
{
if (!(sl->join))
continue;
for (TABLE_LIST *tbl= sl->join->tables_list; tbl; tbl= tbl->next_local)
{
if (!tbl->table)
continue;
return tbl;
}
}
return 0;
}
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