MDEV-17785: Window functions not working in ONLY_FULL_GROUP_BY mode

(Backport Varun Gupta's patch + edit the commit comment)

Name resolution code produced errors for valid queries with window
functions (but not for queries which used aggregate functions as
window functions).

Name resolution code worked incorrectly, because window function
objects had is_window_func_sum_expr()=false. This was so, because
mark_as_window_func_sum_expr() was only called for aggregate functions
used as window functions.

The fix is to call it for any window function.

mysql-test/r/win.result

@@ -4198,5 +4198,37 @@ drop procedure sp7;
 drop view v1,v2;
 drop table t1;
 #
+# MDEV-17785: Window functions not working in ONLY_FULL_GROUP_BY mode
+#
+CREATE TABLE t1(a VARCHAR(10), b int);
+INSERT INTO t1 VALUES
+('Maths', 60),('Maths', 60),
+('Maths', 70),('Maths', 55),
+('Biology', 60), ('Biology', 70);
+SET @save_sql_mode= @@sql_mode;
+SET sql_mode = 'ONLY_FULL_GROUP_BY';
+SELECT
+RANK() OVER (PARTITION BY a ORDER BY b) AS rank,
+a, b FROM t1 ORDER BY a, b DESC;
+rank	a	b
+2	Biology	70
+1	Biology	60
+4	Maths	70
+2	Maths	60
+2	Maths	60
+1	Maths	55
+SET sql_mode= @save_sql_mode;
+DROP TABLE t1;
+CREATE TABLE t1(i int,j int);
+INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
+INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
+SELECT i, LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j) FROM t1 GROUP BY i;
+i	LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j)
+1	6
+2	4
+3	2
+4	2
+DROP TABLE t1;
+#
 # End of 10.2 tests
 #

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

@@ -4204,6 +4204,38 @@ drop procedure sp7;
 drop view v1,v2;
 drop table t1;
 #
+# MDEV-17785: Window functions not working in ONLY_FULL_GROUP_BY mode
+#
+CREATE TABLE t1(a VARCHAR(10), b int);
+INSERT INTO t1 VALUES
+('Maths', 60),('Maths', 60),
+('Maths', 70),('Maths', 55),
+('Biology', 60), ('Biology', 70);
+SET @save_sql_mode= @@sql_mode;
+SET sql_mode = 'ONLY_FULL_GROUP_BY';
+SELECT
+RANK() OVER (PARTITION BY a ORDER BY b) AS rank,
+a, b FROM t1 ORDER BY a, b DESC;
+rank	a	b
+2	Biology	70
+1	Biology	60
+4	Maths	70
+2	Maths	60
+2	Maths	60
+1	Maths	55
+SET sql_mode= @save_sql_mode;
+DROP TABLE t1;
+CREATE TABLE t1(i int,j int);
+INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
+INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
+SELECT i, LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j) FROM t1 GROUP BY i;
+i	LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j)
+1	6
+2	4
+3	2
+4	2
+DROP TABLE t1;
+#
 # End of 10.2 tests
 #
 #

mysql-test/t/win.test

@@ -2703,6 +2703,33 @@ drop procedure sp7;
 drop view v1,v2;
 drop table t1;
 
+--echo #
+--echo # MDEV-17785: Window functions not working in ONLY_FULL_GROUP_BY mode
+--echo #
+
+CREATE TABLE t1(a VARCHAR(10), b int);
+
+INSERT INTO t1 VALUES
+('Maths', 60),('Maths', 60),
+('Maths', 70),('Maths', 55),
+('Biology', 60), ('Biology', 70);
+
+SET @save_sql_mode= @@sql_mode;
+SET sql_mode = 'ONLY_FULL_GROUP_BY';
+
+SELECT
+  RANK() OVER (PARTITION BY a ORDER BY b) AS rank,
+  a, b FROM t1 ORDER BY a, b DESC;
+
+SET sql_mode= @save_sql_mode;
+DROP TABLE t1;
+
+CREATE TABLE t1(i int,j int);
+INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
+INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
+SELECT i, LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j) FROM t1 GROUP BY i;
+DROP TABLE t1;
+
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/item_windowfunc.cc

@@ -93,6 +93,9 @@ Item_window_func::fix_fields(THD *thd, Item **ref)
     my_error(ER_NO_ORDER_LIST_IN_WINDOW_SPEC, MYF(0), window_func()->func_name());
     return true;
   }
+
+  window_func()->mark_as_window_func_sum_expr();
+
   /*
     TODO: why the last parameter is 'ref' in this call? What if window_func
     decides to substitute itself for something else and does *ref=.... ? 

sql/sql_yacc.yy

@@ -10557,9 +10557,6 @@ window_func:
           simple_window_func
         |
           sum_expr
-          {
-            ((Item_sum *) $1)->mark_as_window_func_sum_expr();
-          }
         ;
 
 simple_window_func: