Fixed bug mdev-4918.

The function SELECT_LEX::mark_const_derived() must take into account that
in DELETE ... RETURNING join == NULL.

mysql-test/r/delete_returning.result

@@ -233,3 +233,13 @@ DROP USER mysqltest_1@localhost;
 DROP VIEW v1;
 DROP TABLE t1,t2;
 DROP TABLE t1c,t2c;
+#
+# Bug mdev-4918: DELETE ... RETURNING subquery with more than 1 row
+#
+CREATE TABLE t1 (i1 int);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (i2 int);
+INSERT INTO t2 VALUES (1),(2);
+DELETE FROM t1 ORDER BY i1 RETURNING ( SELECT i2 FROM t2 );
+ERROR 21000: Subquery returns more than 1 row
+DROP TABLE t1,t2;

mysql-test/t/delete_returning.test

@@ -186,4 +186,17 @@ DROP VIEW v1;
 DROP TABLE t1,t2;
 DROP TABLE t1c,t2c;
 
+--echo #
+--echo # Bug mdev-4918: DELETE ... RETURNING subquery with more than 1 row
+--echo #
 
+CREATE TABLE t1 (i1 int);
+INSERT INTO t1 VALUES (1),(2);
+
+CREATE TABLE t2 (i2 int);
+INSERT INTO t2 VALUES (1),(2);
+
+--error ER_SUBQUERY_NO_1_ROW
+DELETE FROM t1 ORDER BY i1 RETURNING ( SELECT i2 FROM t2 );
+
+DROP TABLE t1,t2;
\ No newline at end of file

sql/sql_lex.cc

@@ -4085,7 +4085,8 @@ void SELECT_LEX::increase_derived_records(ha_rows records)
 void SELECT_LEX::mark_const_derived(bool empty)
 {
   TABLE_LIST *derived= master_unit()->derived;
-  if (!join->thd->lex->describe && derived)
+  /* join == NULL in  DELETE ... RETURNING */
+  if (!(join && join->thd->lex->describe) && derived)
   {
     if (!empty)
       increase_derived_records(1);