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mariadb/sql/opt_subselect.h
Galina Shalygina 7a77b221f1 MDEV-7486: Condition pushdown from HAVING into WHERE 
Condition can be pushed from the HAVING clause into the WHERE clause
if it depends only on the fields that are used in the GROUP BY list
or depends on the fields that are equal to grouping fields.
Aggregate functions can't be pushed down.

How the pushdown is performed on the example:

SELECT t1.a,MAX(t1.b)
FROM t1
GROUP BY t1.a
HAVING (t1.a>2) AND (MAX(c)>12);

=>

SELECT t1.a,MAX(t1.b)
FROM t1
WHERE (t1.a>2)
GROUP BY t1.a
HAVING (MAX(c)>12);

The implementation scheme:

1. Extract the most restrictive condition cond from the HAVING clause of
   the select that depends only on the fields that are used in the GROUP BY
   list of the select (directly or indirectly through equalities)
2. Save cond as a condition that can be pushed into the WHERE clause
   of the select
3. Remove cond from the HAVING clause if it is possible

The optimization is implemented in the function
st_select_lex::pushdown_from_having_into_where().

New test file having_cond_pushdown.test is created.
2019-02-17 23:38:44 -08:00

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/*
Copyright (c) 2010, 2015, 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 Street, Fifth Floor, Boston, MA 02111-1301 USA */
/*
Semi-join subquery optimization code definitions
*/
#ifdef USE_PRAGMA_INTERFACE
#pragma interface /* gcc class implementation */
#endif
int check_and_do_in_subquery_rewrites(JOIN *join);
bool convert_join_subqueries_to_semijoins(JOIN *join);
int pull_out_semijoin_tables(JOIN *join);
bool optimize_semijoin_nests(JOIN *join, table_map all_table_map);
bool setup_degenerate_jtbm_semi_joins(JOIN *join,
List<TABLE_LIST> *join_list,
List<Item> &eq_list);
bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,
List<Item> &eq_list);
void cleanup_empty_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list);
// used by Loose_scan_opt
ulonglong get_bound_sj_equalities(TABLE_LIST *sj_nest,
table_map remaining_tables);
/*
This is a class for considering possible loose index scan optimizations.
It's usage pattern is as follows:
best_access_path()
{
Loose_scan_opt opt;
opt.init()
for each index we can do ref access with
{
opt.next_ref_key();
for each keyuse
opt.add_keyuse();
opt.check_ref_access();
}
if (some criteria for range scans)
opt.check_range_access();
opt.get_best_option();
}
*/
class Loose_scan_opt
{
/* All methods must check this before doing anything else */
bool try_loosescan;
/*
If we consider (oe1, .. oeN) IN (SELECT ie1, .. ieN) then ieK=oeK is
called sj-equality. If oeK depends only on preceding tables then such
equality is called 'bound'.
*/
ulonglong bound_sj_equalities;
/* Accumulated properties of ref access we're now considering: */
ulonglong handled_sj_equalities;
key_part_map loose_scan_keyparts;
uint max_loose_keypart;
bool part1_conds_met;
/*
Use of quick select is a special case. Some of its properties:
*/
uint quick_uses_applicable_index;
uint quick_max_loose_keypart;
/* Best loose scan method so far */
uint best_loose_scan_key;
double best_loose_scan_cost;
double best_loose_scan_records;
KEYUSE *best_loose_scan_start_key;
uint best_max_loose_keypart;
public:
Loose_scan_opt():
try_loosescan(FALSE),
bound_sj_equalities(0),
quick_uses_applicable_index(FALSE)
{
/* Protected by quick_uses_applicable_index */
LINT_INIT(quick_max_loose_keypart);
/* The following are protected by best_loose_scan_cost!= DBL_MAX */
LINT_INIT(best_loose_scan_key);
LINT_INIT(best_loose_scan_records);
LINT_INIT(best_max_loose_keypart);
LINT_INIT(best_loose_scan_start_key);
}
void init(JOIN *join, JOIN_TAB *s, table_map remaining_tables)
{
/*
Discover the bound equalities. We need to do this if
1. The next table is an SJ-inner table, and
2. It is the first table from that semijoin, and
3. We're not within a semi-join range (i.e. all semi-joins either have
all or none of their tables in join_table_map), except
s->emb_sj_nest (which we've just entered, see #2).
4. All non-IN-equality correlation references from this sj-nest are
bound
5. But some of the IN-equalities aren't (so this can't be handled by
FirstMatch strategy)
*/
best_loose_scan_cost= DBL_MAX;
if (!join->emb_sjm_nest && s->emb_sj_nest && // (1)
s->emb_sj_nest->sj_in_exprs < 64 &&
((remaining_tables & s->emb_sj_nest->sj_inner_tables) == // (2)
s->emb_sj_nest->sj_inner_tables) && // (2)
join->cur_sj_inner_tables == 0 && // (3)
!(remaining_tables &
s->emb_sj_nest->nested_join->sj_corr_tables) && // (4)
remaining_tables & s->emb_sj_nest->nested_join->sj_depends_on &&// (5)
optimizer_flag(join->thd, OPTIMIZER_SWITCH_LOOSE_SCAN))
{
/* This table is an LooseScan scan candidate */
bound_sj_equalities= get_bound_sj_equalities(s->emb_sj_nest,
remaining_tables);
try_loosescan= TRUE;
DBUG_PRINT("info", ("Will try LooseScan scan, bound_map=%llx",
(longlong)bound_sj_equalities));
}
}
void next_ref_key()
{
handled_sj_equalities=0;
loose_scan_keyparts= 0;
max_loose_keypart= 0;
part1_conds_met= FALSE;
}
void add_keyuse(table_map remaining_tables, KEYUSE *keyuse)
{
if (try_loosescan && keyuse->sj_pred_no != UINT_MAX &&
(keyuse->table->file->index_flags(keyuse->key, 0, 1 ) & HA_READ_ORDER))
{
if (!(remaining_tables & keyuse->used_tables))
{
/*
This allows to use equality propagation to infer that some
sj-equalities are bound.
*/
bound_sj_equalities |= 1ULL << keyuse->sj_pred_no;
}
else
{
handled_sj_equalities |= 1ULL << keyuse->sj_pred_no;
loose_scan_keyparts |= ((key_part_map)1) << keyuse->keypart;
set_if_bigger(max_loose_keypart, keyuse->keypart);
}
}
}
bool have_a_case() { return MY_TEST(handled_sj_equalities); }
void check_ref_access_part1(JOIN_TAB *s, uint key, KEYUSE *start_key,
table_map found_part)
{
/*
Check if we can use LooseScan semi-join strategy. We can if
1. This is the right table at right location
2. All IN-equalities are either
- "bound", ie. the outer_expr part refers to the preceding tables
- "handled", ie. covered by the index we're considering
3. Index order allows to enumerate subquery's duplicate groups in
order. This happens when the index definition matches this
pattern:
(handled_col|bound_col)* (other_col|bound_col)
*/
if (try_loosescan && // (1)
(handled_sj_equalities | bound_sj_equalities) == // (2)
PREV_BITS(ulonglong, s->emb_sj_nest->sj_in_exprs) && // (2)
(PREV_BITS(key_part_map, max_loose_keypart+1) & // (3)
(found_part | loose_scan_keyparts)) == // (3)
PREV_BITS(key_part_map, max_loose_keypart+1) && // (3)
!key_uses_partial_cols(s->table->s, key))
{
if (s->quick && s->quick->index == key &&
s->quick->get_type() == QUICK_SELECT_I::QS_TYPE_RANGE)
{
quick_uses_applicable_index= TRUE;
quick_max_loose_keypart= max_loose_keypart;
}
DBUG_PRINT("info", ("Can use LooseScan scan"));
if (found_part & 1)
{
/* Can use LooseScan on ref access if the first key part is bound */
part1_conds_met= TRUE;
}
/*
Check if this is a special case where there are no usable bound
IN-equalities, i.e. we have
outer_expr IN (SELECT innertbl.key FROM ...)
and outer_expr cannot be evaluated yet, so it's actually full
index scan and not a ref access.
We can do full index scan if it uses index-only.
*/
if (!(found_part & 1 ) && /* no usable ref access for 1st key part */
s->table->covering_keys.is_set(key))
{
part1_conds_met= TRUE;
DBUG_PRINT("info", ("Can use full index scan for LooseScan"));
/* Calculate the cost of complete loose index scan. */
double records= rows2double(s->table->file->stats.records);
/* The cost is entire index scan cost (divided by 2) */
double read_time= s->table->file->keyread_time(key, 1,
(ha_rows) records);
/*
Now find out how many different keys we will get (for now we
ignore the fact that we have "keypart_i=const" restriction for
some key components, that may make us think think that loose
scan will produce more distinct records than it actually will)
*/
ulong rpc;
if ((rpc= s->table->key_info[key].rec_per_key[max_loose_keypart]))
records= records / rpc;
// TODO: previous version also did /2
if (read_time < best_loose_scan_cost)
{
best_loose_scan_key= key;
best_loose_scan_cost= read_time;
best_loose_scan_records= records;
best_max_loose_keypart= max_loose_keypart;
best_loose_scan_start_key= start_key;
}
}
}
}
void check_ref_access_part2(uint key, KEYUSE *start_key, double records,
double read_time)
{
if (part1_conds_met && read_time < best_loose_scan_cost)
{
/* TODO use rec-per-key-based fanout calculations */
best_loose_scan_key= key;
best_loose_scan_cost= read_time;
best_loose_scan_records= records;
best_max_loose_keypart= max_loose_keypart;
best_loose_scan_start_key= start_key;
}
}
void check_range_access(JOIN *join, uint idx, QUICK_SELECT_I *quick)
{
/* TODO: this the right part restriction: */
if (quick_uses_applicable_index && idx == join->const_tables &&
quick->read_time < best_loose_scan_cost)
{
best_loose_scan_key= quick->index;
best_loose_scan_cost= quick->read_time;
/* this is ok because idx == join->const_tables */
best_loose_scan_records= rows2double(quick->records);
best_max_loose_keypart= quick_max_loose_keypart;
best_loose_scan_start_key= NULL;
}
}
void save_to_position(JOIN_TAB *tab, POSITION *pos)
{
pos->read_time= best_loose_scan_cost;
if (best_loose_scan_cost != DBL_MAX)
{
pos->records_read= best_loose_scan_records;
pos->key= best_loose_scan_start_key;
pos->cond_selectivity= 1.0;
pos->loosescan_picker.loosescan_key= best_loose_scan_key;
pos->loosescan_picker.loosescan_parts= best_max_loose_keypart + 1;
pos->use_join_buffer= FALSE;
pos->table= tab;
pos->range_rowid_filter_info= tab->range_rowid_filter_info;
// todo need ref_depend_map ?
DBUG_PRINT("info", ("Produced a LooseScan plan, key %s, %s",
tab->table->key_info[best_loose_scan_key].name.str,
best_loose_scan_start_key? "(ref access)":
"(range/index access)"));
}
}
};
void advance_sj_state(JOIN *join, table_map remaining_tables, uint idx,
double *current_record_count, double *current_read_time,
POSITION *loose_scan_pos);
void restore_prev_sj_state(const table_map remaining_tables,
const JOIN_TAB *tab, uint idx);
void fix_semijoin_strategies_for_picked_join_order(JOIN *join);
bool setup_sj_materialization_part1(JOIN_TAB *sjm_tab);
bool setup_sj_materialization_part2(JOIN_TAB *sjm_tab);
/*
Temporary table used by semi-join DuplicateElimination strategy
This consists of the temptable itself and data needed to put records
into it. The table's DDL is as follows:
CREATE TABLE tmptable (col VARCHAR(n) BINARY, PRIMARY KEY(col));
where the primary key can be replaced with unique constraint if n exceeds
the limit (as it is always done for query execution-time temptables).
The record value is a concatenation of rowids of tables from the join we're
executing. If a join table is on the inner side of the outer join, we
assume that its rowid can be NULL and provide means to store this rowid in
the tuple.
*/
class SJ_TMP_TABLE : public Sql_alloc
{
public:
/*
Array of pointers to tables whose rowids compose the temporary table
record.
*/
class TAB
{
public:
JOIN_TAB *join_tab;
uint rowid_offset;
ushort null_byte;
uchar null_bit;
};
TAB *tabs;
TAB *tabs_end;
/*
is_degenerate==TRUE means this is a special case where the temptable record
has zero length (and presence of a unique key means that the temptable can
have either 0 or 1 records).
In this case we don't create the physical temptable but instead record
its state in SJ_TMP_TABLE::have_degenerate_row.
*/
bool is_degenerate;
/*
When is_degenerate==TRUE: the contents of the table (whether it has the
record or not).
*/
bool have_degenerate_row;
/* table record parameters */
uint null_bits;
uint null_bytes;
uint rowid_len;
/* The temporary table itself (NULL means not created yet) */
TABLE *tmp_table;
/*
These are the members we got from temptable creation code. We'll need
them if we'll need to convert table from HEAP to MyISAM/Maria.
*/
TMP_ENGINE_COLUMNDEF *start_recinfo;
TMP_ENGINE_COLUMNDEF *recinfo;
SJ_TMP_TABLE *next_flush_table;
int sj_weedout_delete_rows();
int sj_weedout_check_row(THD *thd);
bool create_sj_weedout_tmp_table(THD *thd);
};
int setup_semijoin_loosescan(JOIN *join);
int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
uint no_jbuf_after);
void destroy_sj_tmp_tables(JOIN *join);
int clear_sj_tmp_tables(JOIN *join);
int rewrite_to_index_subquery_engine(JOIN *join);
void get_delayed_table_estimates(TABLE *table,
ha_rows *out_rows,
double *scan_time,
double *startup_cost);
enum_nested_loop_state join_tab_execution_startup(JOIN_TAB *tab);
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