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

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.

Author: varunraiko

mysql-test/r/subselect4.result

@@ -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;

mysql-test/t/subselect4.test

@@ -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;

sql/item_subselect.cc

@@ -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();