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Commit 218a96d2 authored by igor@rurik.mysql.com's avatar igor@rurik.mysql.com
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Fixed bug #21390: wrong estimate of rows after elimination of 

const tables. This resulted in choosing extremely inefficient
execution plans in same cases when distribution of data in
joined were skewed (see the customer test case for the bug).
parent 7240c97d
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Showing with 135 additions and 26 deletions
mysql-test/r/select.result
View file @ 218a96d2
......@@ -2328,9 +2328,9 @@ explain select * from t1 left join t2 on id1 = id2 left join t3 on id1 = id3
left join t4 on id3 = id4 where id2 = 1 or id4 = 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 system NULL NULL NULL NULL 0 const row not found
1 SIMPLE t4 const id4 NULL NULL NULL 1
1 SIMPLE t1 ALL NULL NULL NULL NULL 2
1 SIMPLE t2 ALL NULL NULL NULL NULL 1
1 SIMPLE t4 ALL id4 NULL NULL NULL 1 Using where
1 SIMPLE t2 ALL NULL NULL NULL NULL 1 Using where
select * from t1 left join t2 on id1 = id2 left join t3 on id1 = id3
left join t4 on id3 = id4 where id2 = 1 or id4 = 1;
id1 id2 id3 id4 id44
......@@ -3479,3 +3479,41 @@ Warning 1466 Leading spaces are removed from name ' a '
execute stmt;
a
1
CREATE TABLE t1 (a int NOT NULL PRIMARY KEY, b int NOT NULL);
INSERT INTO t1 VALUES (1,1), (2,2), (3,3), (4,4);
CREATE TABLE t2 (c int NOT NULL, INDEX idx(c));
INSERT INTO t2 VALUES
(1), (1), (1), (1), (1), (1), (1), (1),
(2), (2), (2), (2),
(3), (3),
(4);
EXPLAIN SELECT b FROM t1, t2 WHERE b=c AND a=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const PRIMARY PRIMARY 4 const 1
1 SIMPLE t2 ref idx idx 4 const 7 Using index
EXPLAIN SELECT b FROM t1, t2 WHERE b=c AND a=4;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const PRIMARY PRIMARY 4 const 1
1 SIMPLE t2 ref idx idx 4 const 1 Using index
DROP TABLE t1, t2;
CREATE TABLE t1 (id int NOT NULL PRIMARY KEY, a int);
INSERT INTO t1 VALUES (1,2), (2,NULL), (3,2);
CREATE TABLE t2 (b int, c INT, INDEX idx1(b));
INSERT INTO t2 VALUES (2,1), (3,2);
CREATE TABLE t3 (d int, e int, INDEX idx1(d));
INSERT INTO t3 VALUES (2,10), (2,20), (1,30), (2,40), (2,50);
EXPLAIN
SELECT * FROM t1 LEFT JOIN t2 ON t2.b=t1.a INNER JOIN t3 ON t3.d=t1.id
WHERE t1.id=2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const PRIMARY PRIMARY 4 const 1
1 SIMPLE t2 const idx1 NULL NULL NULL 1
1 SIMPLE t3 ref idx1 idx1 5 const 3 Using where
SELECT * FROM t1 LEFT JOIN t2 ON t2.b=t1.a INNER JOIN t3 ON t3.d=t1.id
WHERE t1.id=2;
id a b c d e
2 NULL NULL NULL 2 10
2 NULL NULL NULL 2 20
2 NULL NULL NULL 2 40
2 NULL NULL NULL 2 50
DROP TABLE t1,t2,t3;
mysql-test/t/select.test
View file @ 218a96d2
......@@ -2957,3 +2957,44 @@ SELECT 0.9888889889 * 1.011111411911;
#
prepare stmt from 'select 1 as " a "';
execute stmt;
#
# Bug #21390: wrong estimate of rows after elimination of const tables
#
CREATE TABLE t1 (a int NOT NULL PRIMARY KEY, b int NOT NULL);
INSERT INTO t1 VALUES (1,1), (2,2), (3,3), (4,4);
CREATE TABLE t2 (c int NOT NULL, INDEX idx(c));
INSERT INTO t2 VALUES
(1), (1), (1), (1), (1), (1), (1), (1),
(2), (2), (2), (2),
(3), (3),
(4);
EXPLAIN SELECT b FROM t1, t2 WHERE b=c AND a=1;
EXPLAIN SELECT b FROM t1, t2 WHERE b=c AND a=4;
DROP TABLE t1, t2;
#
# No matches for a join after substitution of a const table
#
CREATE TABLE t1 (id int NOT NULL PRIMARY KEY, a int);
INSERT INTO t1 VALUES (1,2), (2,NULL), (3,2);
CREATE TABLE t2 (b int, c INT, INDEX idx1(b));
INSERT INTO t2 VALUES (2,1), (3,2);
CREATE TABLE t3 (d int, e int, INDEX idx1(d));
INSERT INTO t3 VALUES (2,10), (2,20), (1,30), (2,40), (2,50);
EXPLAIN
SELECT * FROM t1 LEFT JOIN t2 ON t2.b=t1.a INNER JOIN t3 ON t3.d=t1.id
WHERE t1.id=2;
SELECT * FROM t1 LEFT JOIN t2 ON t2.b=t1.a INNER JOIN t3 ON t3.d=t1.id
WHERE t1.id=2;
DROP TABLE t1,t2,t3;
sql/sql_select.cc
View file @ 218a96d2
......@@ -2205,6 +2205,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables, COND *conds,
int ref_changed;
do
{
more_const_tables_found:
ref_changed = 0;
found_ref=0;
......@@ -2216,6 +2217,30 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables, COND *conds,
for (JOIN_TAB **pos=stat_vector+const_count ; (s= *pos) ; pos++)
{
table=s->table;
/*
If equi-join condition by a key is null rejecting and after a
substitution of a const table the key value happens to be null
then we can state that there are no matches for this equi-join.
*/
if ((keyuse= s->keyuse) && *s->on_expr_ref)
{
while (keyuse->table == table)
{
if (!(keyuse->val->used_tables() & ~join->const_table_map) &&
keyuse->val->is_null() && keyuse->null_rejecting)
{
s->type= JT_CONST;
mark_as_null_row(table);
found_const_table_map|= table->map;
join->const_table_map|= table->map;
set_position(join,const_count++,s,(KEYUSE*) 0);
goto more_const_tables_found;
}
keyuse++;
}
}
if (s->dependent) // If dependent on some table
{
// All dep. must be constants
......@@ -2266,34 +2291,38 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables, COND *conds,
} while (keyuse->table == table && keyuse->key == key);
if (eq_part.is_prefix(table->key_info[key].key_parts) &&
((table->key_info[key].flags & (HA_NOSAME | HA_END_SPACE_KEY)) ==
HA_NOSAME) &&
!table->fulltext_searched &&
!table->pos_in_table_list->embedding)
{
if (const_ref == eq_part)
{ // Found everything for ref.
int tmp;
ref_changed = 1;
s->type= JT_CONST;
join->const_table_map|=table->map;
set_position(join,const_count++,s,start_keyuse);
if (create_ref_for_key(join, s, start_keyuse,
found_const_table_map))
DBUG_RETURN(1);
if ((tmp=join_read_const_table(s,
join->positions+const_count-1)))
{
if (tmp > 0)
DBUG_RETURN(1); // Fatal error
if ((table->key_info[key].flags & (HA_NOSAME | HA_END_SPACE_KEY))
== HA_NOSAME)
{
if (const_ref == eq_part)
{ // Found everything for ref.
int tmp;
ref_changed = 1;
s->type= JT_CONST;
join->const_table_map|=table->map;
set_position(join,const_count++,s,start_keyuse);
if (create_ref_for_key(join, s, start_keyuse,
found_const_table_map))
DBUG_RETURN(1);
if ((tmp=join_read_const_table(s,
join->positions+const_count-1)))
{
if (tmp > 0)
DBUG_RETURN(1); // Fatal error
}
else
found_const_table_map|= table->map;
break;
}
else
found_const_table_map|= table->map;
break;
found_ref|= refs; // Table is const if all refs are const
}
else
found_ref|= refs; // Table is const if all refs are const
}
else if (const_ref == eq_part)
s->const_keys.set_bit(key);
}
}
}
}
......@@ -2696,7 +2725,8 @@ add_key_field(KEY_FIELD **key_fields,uint and_level, Item_func *cond,
We use null_rejecting in add_not_null_conds() to add
'othertbl.field IS NOT NULL' to tab->select_cond.
*/
(*key_fields)->null_rejecting= ((cond->functype() == Item_func::EQ_FUNC) &&
(*key_fields)->null_rejecting= ((cond->functype() == Item_func::EQ_FUNC ||
cond->functype() == Item_func::MULT_EQUAL_FUNC) &&
((*value)->type() == Item::FIELD_ITEM) &&
((Item_field*)*value)->field->maybe_null());
(*key_fields)++;
......@@ -3461,7 +3491,7 @@ best_access_path(JOIN *join,
keyuse->used_tables));
if (tmp < best_prev_record_reads)
{
best_part_found_ref= keyuse->used_tables;
best_part_found_ref= keyuse->used_tables & ~join->const_table_map;
best_prev_record_reads= tmp;
}
if (rec > keyuse->ref_table_rows)
......
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