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MDEV-16820 Lost 'Impossible where' from query with inexpensive subquery

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This patch fixes another problem introduced by the patch for mdev-4817.
The latter changed Item_cond::fix_fields() in such a way that it could
call the virtual method is_expensive(). With the first its call
the method saves the result in Item::is_expensive_cache. For all next
calls the method returns the result from this cache. So if the item
once was determined as expensive the method always returns true.
For subqueries it's not good, because non-optimized subqueries always
is considered as expensive.
It means that the cache should be invalidated after the call of
optimize_constant_subqueries().
This commit is contained in:
Igor Babaev
2018-07-25 11:57:57 -07:00
parent de85355436
commit aad70e9b4c
9 changed files with 123 additions and 0 deletions
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16
mysql-test/r/subselect.result
View File

@ -7240,6 +7240,22 @@ a
5
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
#
# MDEV-16820: impossible where with inexpensive subquery
#
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1,t2;
End of 5.5 tests
# End of 10.0 tests
#

16
mysql-test/r/subselect_no_exists_to_in.result
View File

@ -7240,6 +7240,22 @@ a
5
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
#
# MDEV-16820: impossible where with inexpensive subquery
#
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1,t2;
End of 5.5 tests
# End of 10.0 tests
#

16
mysql-test/r/subselect_no_mat.result
View File

@ -7233,6 +7233,22 @@ a
5
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
#
# MDEV-16820: impossible where with inexpensive subquery
#
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1,t2;
End of 5.5 tests
# End of 10.0 tests
#

16
mysql-test/r/subselect_no_opts.result
View File

@ -7231,6 +7231,22 @@ a
5
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
#
# MDEV-16820: impossible where with inexpensive subquery
#
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1,t2;
End of 5.5 tests
# End of 10.0 tests
#

16
mysql-test/r/subselect_no_scache.result
View File

@ -7246,6 +7246,22 @@ a
5
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
#
# MDEV-16820: impossible where with inexpensive subquery
#
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1,t2;
End of 5.5 tests
# End of 10.0 tests
#

16
mysql-test/r/subselect_no_semijoin.result
View File

@ -7231,6 +7231,22 @@ a
5
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
#
# MDEV-16820: impossible where with inexpensive subquery
#
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1,t2;
End of 5.5 tests
# End of 10.0 tests
#

15
mysql-test/t/subselect.test
View File

@ -6102,6 +6102,21 @@ and t1.a in (select `test`.`t3`.`c` from `test`.`t3`);
SET @@optimizer_switch= @optimiser_switch_save;
DROP TABLE t1, t2, t3;
--echo #
--echo # MDEV-16820: impossible where with inexpensive subquery
--echo #
create table t1 (a int) engine=myisam;
insert into t1 values (3), (1), (7);
create table t2 (b int, index idx(b));
insert into t2 values (2), (5), (3), (2);
explain select * from t1 where (select max(b) from t2) = 10;
explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
drop table t1,t2;
--echo End of 5.5 tests
--echo # End of 10.0 tests

5
sql/item.h
View File

@ -1614,6 +1614,11 @@ public:
virtual bool limit_index_condition_pushdown_processor(void *arg) { return 0; }
virtual bool exists2in_processor(void *arg) { return 0; }
virtual bool find_selective_predicates_list_processor(void *arg) { return 0; }
bool cleanup_is_expensive_cache_processor(void *arg)
{
is_expensive_cache= (int8)(-1);
return 0;
}
/*
TRUE if the expression depends only on the table indicated by tab_map

7
sql/sql_select.cc
View File

@ -1335,6 +1335,13 @@ JOIN::optimize_inner()
if (optimize_constant_subqueries())
DBUG_RETURN(1);
if (conds && conds->has_subquery())
(void) conds->walk(&Item::cleanup_is_expensive_cache_processor,
0, (void *) 0);
if (having && having->has_subquery())
(void) having->walk(&Item::cleanup_is_expensive_cache_processor,
0, (void *) 0);
if (setup_jtbm_semi_joins(this, join_list, &conds))
DBUG_RETURN(1);