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MDEV-30538 Plans for SELECT and multi-table UPDATE/DELETE unexpectedly differ
This patch allowed transformation of EXISTS subqueries into equivalent IN predicands at the top level of WHERE conditions for multi-table UPDATE and DELETE statements. There was no reason to prohibit the transformation for such statements. The transformation provides more opportunities of using semi-join optimizations. Approved by Oleksandr Byelkin <sanja@mariadb.com>
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‎mysql-test/main/multi_update.result

Lines changed: 120 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1251,3 +1251,123 @@ EXPLAIN
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}
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}
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DROP TABLES t1, t2;
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# End of 10.3 tests
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#
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# MDEV-28538: multi-table UPDATE/DELETE with possible exists-to-in
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#
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create table t1 (c1 int, c2 int, c3 int, index idx(c2));
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insert into t1 values
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(1,1,1),(3,2,2),(1,3,3),
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(2,1,4),(2,2,5),(4,3,6),
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(2,4,7),(2,5,8);
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create table t2 (c1 int, c2 int, c3 int, index idx(c2));
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insert into t2 values
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(1,7,1),(1,8,2),(1,3,3),
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(2,1,4),(2,2,5),(2,3,6),
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(2,4,7),(2,5,8);
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create table t3 (c1 int, c2 int, c3 int, index idx(c2));
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insert into t3 values
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(1,1,1),(1,2,2),(1,3,3),
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(2,1,4),(2,2,5),(2,3,6),
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(2,4,7),(2,5,8);
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insert into t3 select c1+1, c2+2, c3 from t3;
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insert into t3 select c1, c2+2, c3 from t3;
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analyze table t1,t2,t3 persistent for all;
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Table Op Msg_type Msg_text
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test.t1 analyze status Engine-independent statistics collected
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test.t1 analyze status OK
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test.t2 analyze status Engine-independent statistics collected
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test.t2 analyze status OK
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test.t3 analyze status Engine-independent statistics collected
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test.t3 analyze status OK
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explain select * from t1,t3
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where t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 ALL idx NULL NULL NULL 8 Using where
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1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
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1 PRIMARY t3 ref idx idx 5 test.t1.c2 3
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2 MATERIALIZED t2 range idx idx 5 NULL 3 Using index condition; Using where
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explain delete from t1 using t1,t3
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where t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 ALL idx NULL NULL NULL 8 Using where
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1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
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1 PRIMARY t3 ref idx idx 5 test.t1.c2 3 Using index
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2 MATERIALIZED t2 range idx idx 5 NULL 3 Using where
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explain update t1,t3 set t1.c1 = t1.c1+10
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where t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 ALL idx NULL NULL NULL 8 Using where
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1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
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1 PRIMARY t3 ref idx idx 5 test.t1.c2 3 Using index
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2 MATERIALIZED t2 range idx idx 5 NULL 3 Using where
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create table t as select * from t1;
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select * from t1,t3
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where t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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c1 c2 c3 c1 c2 c3
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2 1 4 1 1 1
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2 1 4 2 1 4
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2 2 5 1 2 2
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2 2 5 2 2 5
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2 4 7 2 4 7
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2 4 7 2 4 2
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2 4 7 3 4 5
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2 4 7 1 4 2
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2 4 7 2 4 5
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2 5 8 2 5 8
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2 5 8 2 5 3
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2 5 8 3 5 6
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2 5 8 1 5 3
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2 5 8 2 5 6
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2 5 8 2 5 1
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2 5 8 3 5 4
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select * from t1;
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c1 c2 c3
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1 1 1
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3 2 2
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1 3 3
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2 1 4
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2 2 5
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4 3 6
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2 4 7
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2 5 8
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delete from t1 using t1,t3
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where t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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select * from t1;
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c1 c2 c3
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1 1 1
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3 2 2
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1 3 3
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4 3 6
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truncate table t1;
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insert into t1 select * from t;
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analyze table t1 persistent for all;
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Table Op Msg_type Msg_text
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test.t1 analyze status Engine-independent statistics collected
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test.t1 analyze status Table is already up to date
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update t1,t3 set t1.c1 = t1.c1+10
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where t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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select * from t1;
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c1 c2 c3
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1 1 1
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3 2 2
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1 3 3
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12 1 4
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12 2 5
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4 3 6
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12 4 7
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12 5 8
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drop table t1,t2,t3,t;
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# End of 10.4 tests

‎mysql-test/main/multi_update.test

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Original file line numberDiff line numberDiff line change
@@ -1130,3 +1130,73 @@ EXPLAIN FORMAT=JSON UPDATE t2 JOIN t1 USING(a) SET t2.part=2 WHERE t2.part=1 AND
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EXPLAIN FORMAT=JSON UPDATE t2 JOIN t1 USING(a) SET t2.part=3 WHERE t2.part=2 AND t1.part=2;
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DROP TABLES t1, t2;
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--echo # End of 10.3 tests
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--echo #
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--echo # MDEV-28538: multi-table UPDATE/DELETE with possible exists-to-in
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--echo #
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create table t1 (c1 int, c2 int, c3 int, index idx(c2));
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insert into t1 values
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(1,1,1),(3,2,2),(1,3,3),
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(2,1,4),(2,2,5),(4,3,6),
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(2,4,7),(2,5,8);
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create table t2 (c1 int, c2 int, c3 int, index idx(c2));
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insert into t2 values
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(1,7,1),(1,8,2),(1,3,3),
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(2,1,4),(2,2,5),(2,3,6),
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(2,4,7),(2,5,8);
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create table t3 (c1 int, c2 int, c3 int, index idx(c2));
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insert into t3 values
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(1,1,1),(1,2,2),(1,3,3),
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(2,1,4),(2,2,5),(2,3,6),
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(2,4,7),(2,5,8);
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insert into t3 select c1+1, c2+2, c3 from t3;
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insert into t3 select c1, c2+2, c3 from t3;
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analyze table t1,t2,t3 persistent for all;
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let $c=
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t1.c2 = t3.c2 and
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t1.c1 > 1 and
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exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
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let $q1=
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select * from t1,t3
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where $c;
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eval explain $q1;
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let $q2=
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delete from t1 using t1,t3
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where $c;
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eval explain $q2;
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let $q3=
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update t1,t3 set t1.c1 = t1.c1+10
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where $c;
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eval explain $q3;
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create table t as select * from t1;
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eval $q1;
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select * from t1;
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eval $q2;
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select * from t1;
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truncate table t1;
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insert into t1 select * from t;
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analyze table t1 persistent for all;
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eval $q3;
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select * from t1;
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drop table t1,t2,t3,t;
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--echo # End of 10.4 tests

‎mysql-test/main/update_use_source.result

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -76,7 +76,8 @@ rollback;
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explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 ALL NULL NULL NULL NULL 8 Using where
79-
2 DEPENDENT SUBQUERY a ALL NULL NULL NULL NULL 8 Using where
79+
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
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2 MATERIALIZED a ALL NULL NULL NULL NULL 8
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start transaction;
8182
update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
8283
affected rows: 4
@@ -317,7 +318,8 @@ rollback;
317318
explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
318319
id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 range t1_c2 t1_c2 5 NULL 2 Using where
320-
2 DEPENDENT SUBQUERY a ref t1_c2 t1_c2 5 test.t1.c2 4 Using index
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1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
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2 MATERIALIZED a range t1_c2 t1_c2 5 NULL 2 Using where; Using index
321323
start transaction;
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update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
323325
affected rows: 4
@@ -558,7 +560,8 @@ rollback;
558560
explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
559561
id select_type table type possible_keys key key_len ref rows Extra
560562
1 PRIMARY t1 range t1_c2 t1_c2 5 NULL 2 Using where
561-
2 DEPENDENT SUBQUERY a ref t1_c2 t1_c2 5 test.t1.c2 1 Using index
563+
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
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2 MATERIALIZED a range t1_c2 t1_c2 5 NULL 2 Using where; Using index
562565
start transaction;
563566
update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
564567
affected rows: 4
@@ -800,7 +803,8 @@ rollback;
800803
explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
801804
id select_type table type possible_keys key key_len ref rows Extra
802805
1 PRIMARY t1 range t1_c2 t1_c2 5 NULL 2 Using where
803-
2 DEPENDENT SUBQUERY a ref t1_c2 t1_c2 5 test.t1.c2 1 Using index
806+
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
807+
2 MATERIALIZED a range t1_c2 t1_c2 5 NULL 2 Using where; Using index
804808
start transaction;
805809
update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
806810
affected rows: 4

‎sql/item_subselect.cc

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2825,7 +2825,9 @@ bool Item_exists_subselect::select_prepare_to_be_in()
28252825
bool trans_res= FALSE;
28262826
DBUG_ENTER("Item_exists_subselect::select_prepare_to_be_in");
28272827
if (!optimizer &&
2828-
thd->lex->sql_command == SQLCOM_SELECT &&
2828+
(thd->lex->sql_command == SQLCOM_SELECT ||
2829+
thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
2830+
thd->lex->sql_command == SQLCOM_DELETE_MULTI) &&
28292831
!unit->first_select()->is_part_of_union() &&
28302832
optimizer_flag(thd, OPTIMIZER_SWITCH_EXISTS_TO_IN) &&
28312833
(is_top_level_item() ||

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