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MDEV-15555: select from DUAL where false yielding wrong result when in a IN

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For the query having an IN subquery with no tables, we were converting the subquery with an expression between
the left part and the select list of the subquery . This can give incorrect results when we have a condition
in the subquery with a dual table (as this is treated as a no table).

The fix is that we don't do this conversion when we have conds in the subquery with a dual table.
This commit is contained in:
Varun Gupta
2018-03-21 01:34:45 +05:30
parent 69bc3c1976
commit 2dd4e50d5f
3 changed files with 20 additions and 1 deletions
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11
mysql-test/r/subselect4.result
View File

@ -2498,5 +2498,16 @@ FROM t2 WHERE b <= 'quux' GROUP BY field;
field COUNT(DISTINCT c)
0 1
drop table t1,t2;
#
# MDEV-15555: select from DUAL where false yielding wrong result when in a IN
#
explain
SELECT 2 IN (SELECT 2 from DUAL WHERE 1 != 1);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
SELECT 2 IN (SELECT 2 from DUAL WHERE 1 != 1);
2 IN (SELECT 2 from DUAL WHERE 1 != 1)
0
SET optimizer_switch= @@global.optimizer_switch;
set @@tmp_table_size= @@global.tmp_table_size;

8
mysql-test/t/subselect4.test
View File

@ -2035,5 +2035,13 @@ SELECT ( SELECT COUNT(*) FROM t1 WHERE a = c ) AS field, COUNT(DISTINCT c)
FROM t2 WHERE b <= 'quux' GROUP BY field;
drop table t1,t2;
--echo #
--echo # MDEV-15555: select from DUAL where false yielding wrong result when in a IN
--echo #
explain
SELECT 2 IN (SELECT 2 from DUAL WHERE 1 != 1);
SELECT 2 IN (SELECT 2 from DUAL WHERE 1 != 1);
SET optimizer_switch= @@global.optimizer_switch;
set @@tmp_table_size= @@global.tmp_table_size;

2
sql/item_subselect.cc
View File

@ -1746,7 +1746,7 @@ Item_in_subselect::single_value_transformer(JOIN *join)
Item* join_having= join->having ? join->having : join->tmp_having;
if (!(join_having || select_lex->with_sum_func ||
select_lex->group_list.elements) &&
select_lex->table_list.elements == 0 &&
select_lex->table_list.elements == 0 && !join->conds &&
!select_lex->master_unit()->is_union())
{
Item *where_item= (Item*) select_lex->item_list.head();