MDEV-13723: Server crashes in ha_heap::find_unique_row or Assertion `0' failed...

MDEV-13723: Server crashes in ha_heap::find_unique_row or Assertion `0' failed in st_select_lex_unit::optimize with INTERSECT

With INTERSECT/EXCEPT fact that subquery item of IN/ALL/ANY was not assigned value does not mean that temporary table used for calculating unit is empty (records could be deleted).

mysql-test/r/except.result

@@ -525,3 +525,13 @@ t3	CREATE TABLE `t3` (
   `b1` blob DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop tables t1,t2,t3;
+#
+# MDEV-13723: Server crashes in ha_heap::find_unique_row or
+# Assertion `0' failed in st_select_lex_unit::optimize with INTERSECT
+#
+CREATE TABLE t (i INT);
+INSERT INTO t VALUES (1),(2);
+SELECT * FROM t WHERE i != ANY ( SELECT 3 EXCEPT SELECT 3 );
+i
+drop table t;
+# End of 10.3 tests

mysql-test/r/intersect.result

@@ -689,3 +689,4 @@ View	Create View	character_set_client	collation_connection
 v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS (select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1`) union select `__3`.`c` AS `c`,`__3`.`d` AS `d` from ((select `test`.`t2`.`c` AS `c`,`test`.`t2`.`d` AS `d` from `test`.`t2`) intersect (select `test`.`t3`.`e` AS `e`,`test`.`t3`.`f` AS `f` from `test`.`t3`)) `__3` union (select 4 AS `4`,4 AS `4`)	latin1	latin1_swedish_ci
 drop view v1;
 drop tables t1,t2,t3;
+# End of 10.3 tests

mysql-test/t/except.test

@@ -81,3 +81,17 @@ create table t3 (select a,b,b1 from t1) except (select c,d,d1 from t2);
 show create table t3;
 
 drop tables t1,t2,t3;
+
+--echo #
+--echo # MDEV-13723: Server crashes in ha_heap::find_unique_row or
+--echo # Assertion `0' failed in st_select_lex_unit::optimize with INTERSECT
+--echo #
+CREATE TABLE t (i INT);
+INSERT INTO t VALUES (1),(2);
+
+SELECT * FROM t WHERE i != ANY ( SELECT 3 EXCEPT SELECT 3 );
+
+drop table t;
+
+
+--echo # End of 10.3 tests

mysql-test/t/intersect.test

@@ -190,3 +190,4 @@ show create view v1;
 drop view v1;
 drop tables t1,t2,t3;
 
+--echo # End of 10.3 tests

sql/sql_union.cc

@@ -1259,12 +1259,12 @@ bool st_select_lex_unit::optimize()
       {
         item->assigned(0); // We will reinit & rexecute unit
         item->reset();
+      }
       if (table->is_created())
       {
         table->file->ha_delete_all_rows();
         table->file->info(HA_STATUS_VARIABLE);
       }
-      }
       /* re-enabling indexes for next subselect iteration */
       if (union_distinct && table->file->ha_enable_indexes(HA_KEY_SWITCH_ALL))
       {