MDEV-20922: Adding an order by changes the query results

For Item_direct_view_ref , get value from val_* methods
instead of result* family
The val_* methods gets value from the item on which it is referred.

mysql-test/r/group_by.result

@@ -2792,3 +2792,19 @@ SELECT 1 IN ( SELECT COUNT( DISTINCT f2 ) FROM t1 WHERE f1 <= 4 );
 1 IN ( SELECT COUNT( DISTINCT f2 ) FROM t1 WHERE f1 <= 4 )
 0
 drop table t1;
+#
+# MDEV-20922: Adding an order by changes the query results
+#
+CREATE TABLE t1(a int, b int);
+INSERT INTO t1 values (1, 100), (2, 200), (3, 100), (4, 200);
+create view v1 as select a, b+1 as x from t1;
+SELECT x, COUNT(DISTINCT a) AS y FROM v1 GROUP BY x ORDER BY y;
+x	y
+101	2
+201	2
+SELECT b+1 AS x, COUNT(DISTINCT a) AS y FROM t1 GROUP BY x ORDER BY y;
+x	y
+101	2
+201	2
+drop view v1;
+drop table t1;

mysql-test/t/group_by.test

@@ -1915,3 +1915,17 @@ INSERT INTO t1 VALUES (0,'foo'),(1,'bar');
 SELECT 1 IN ( SELECT COUNT( DISTINCT f2 ) FROM t1 WHERE f1 <= 4 );
 drop table t1;
 
+--echo #
+--echo # MDEV-20922: Adding an order by changes the query results
+--echo #
+
+CREATE TABLE t1(a int, b int);
+INSERT INTO t1 values (1, 100), (2, 200), (3, 100), (4, 200);
+
+create view v1 as select a, b+1 as x from t1;
+
+SELECT x, COUNT(DISTINCT a) AS y FROM v1 GROUP BY x ORDER BY y;
+SELECT b+1 AS x, COUNT(DISTINCT a) AS y FROM t1 GROUP BY x ORDER BY y;
+
+drop view v1;
+drop table t1;

sql/item.cc

@@ -8149,6 +8149,46 @@ Item *Item_direct_view_ref::replace_equal_field(THD *thd, uchar *arg)
 }
 
 
+double Item_direct_view_ref::val_result()
+{
+  double tmp=(*ref)->val_result();
+  null_value=(*ref)->null_value;
+  return tmp;
+}
+
+
+longlong Item_direct_view_ref::val_int_result()
+{
+  longlong tmp=(*ref)->val_int_result();
+  null_value=(*ref)->null_value;
+  return tmp;
+}
+
+
+String *Item_direct_view_ref::str_result(String* tmp)
+{
+  tmp=(*ref)->str_result(tmp);
+  null_value=(*ref)->null_value;
+  return tmp;
+}
+
+
+my_decimal *Item_direct_view_ref::val_decimal_result(my_decimal *val)
+{
+  my_decimal *tmp= (*ref)->val_decimal_result(val);
+  null_value=(*ref)->null_value;
+  return tmp;
+}
+
+
+bool Item_direct_view_ref::val_bool_result()
+{
+  bool tmp= (*ref)->val_bool_result();
+  null_value=(*ref)->null_value;
+  return tmp;
+}
+
+
 bool Item_default_value::eq(const Item *item, bool binary_cmp) const
 {
   return item->type() == DEFAULT_VALUE_ITEM && 

sql/item.h

@@ -4477,6 +4477,14 @@ class Item_direct_view_ref :public Item_direct_ref
     item_equal= NULL;
     Item_direct_ref::cleanup();
   }
+  /*
+    TODO move these val_*_result function to Item_dierct_ref (maybe)
+  */
+  double val_result();
+  longlong val_int_result();
+  String *str_result(String* tmp);
+  my_decimal *val_decimal_result(my_decimal *val);
+  bool val_bool_result();
 };