MDEV-35869 Wrong result using degenerated subquery with window function

This bug affected queries containing degenerated single-value subqueries
with window functions. The bug led mostly to wrong results for such
queries.

A subquery is called degenerated if it is of the form (SELECT <expr>...).

For degenerated subqueries of the form (SELECT <expr>) the transformation
   (SELECT <expr>) => <expr>
usually is applied. However if <expr> contains set functions or window
functions such rewriting is not valid for an obvious reason. The code
before this patch erroneously applied the transformation when <expr>
contained window functions and did not contain set functions.

Approved by Rex Johnston <rex.johnston@mariadb.com>

mysql-test/main/win.result

@@ -4601,4 +4601,27 @@ w2_total	w1_total	u
 200	200	2
 DROP VIEW v1;
 DROP TABLE t1;
+#
+# MDEV-35869: degenerated subquery with window function
+#
+CREATE TABLE t1 (a int DEFAULT 10);
+INSERT INTO t1 VALUES (7), (2), (3);
+SELECT * FROM t1 WHERE (SELECT AVG(3)) > 2;
+a
+7
+2
+3
+SELECT * FROM t1 WHERE (SELECT AVG(3) OVER ()) > 2;
+a
+7
+2
+3
+INSERT INTO t1 VALUES((SELECT avg(4) OVER ()));
+SELECT * FROM t1;
+a
+7
+2
+3
+4
+DROP TABLE t1;
 # End of 10.5 tests

mysql-test/main/win.test

@@ -3001,4 +3001,16 @@ eval $q3;
 DROP VIEW v1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-35869: degenerated subquery with window function
+--echo #
+
+CREATE TABLE t1 (a int DEFAULT 10);
+INSERT INTO t1 VALUES (7), (2), (3);
+SELECT * FROM t1 WHERE (SELECT AVG(3)) > 2;
+SELECT * FROM t1 WHERE (SELECT AVG(3) OVER ()) > 2;
+INSERT INTO t1 VALUES((SELECT avg(4) OVER ()));
+SELECT * FROM t1;
+DROP TABLE t1;
+
 --echo # End of 10.5 tests

mysql-test/suite/encryption/r/tempfiles_encrypted.result

@@ -4607,6 +4607,29 @@ w2_total	w1_total	u
 200	200	2
 DROP VIEW v1;
 DROP TABLE t1;
+#
+# MDEV-35869: degenerated subquery with window function
+#
+CREATE TABLE t1 (a int DEFAULT 10);
+INSERT INTO t1 VALUES (7), (2), (3);
+SELECT * FROM t1 WHERE (SELECT AVG(3)) > 2;
+a
+7
+2
+3
+SELECT * FROM t1 WHERE (SELECT AVG(3) OVER ()) > 2;
+a
+7
+2
+3
+INSERT INTO t1 VALUES((SELECT avg(4) OVER ()));
+SELECT * FROM t1;
+a
+7
+2
+3
+4
+DROP TABLE t1;
 # End of 10.5 tests
 #
 # MDEV-23867: select crash in compute_window_func

sql/item_subselect.cc

@@ -1215,6 +1215,7 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
       !select_lex->table_list.elements &&
       select_lex->item_list.elements == 1 &&
       !select_lex->item_list.head()->with_sum_func() &&
+      !select_lex->item_list.head()->with_window_func &&
       /*
 	We can't change name of Item_field or Item_ref, because it will
 	prevent its correct resolving, but we should save name of