Merge epotemkin@bk-internal.mysql.com:/home/bk/mysql-5.0-opt

into  moonbone.local:/mnt/gentoo64/work/28494-bug-5.0-opt-mysql

mysql-test/r/user_var.result

@@ -317,3 +317,10 @@ SHOW COUNT(*) WARNINGS;
 SHOW COUNT(*) ERRORS;
 @@session.error_count
 1
+create table t1(f1 int);
+insert into t1 values(1),(1),(2);
+select @a:=f1, count(f1) from t1 group by 1;
+@a:=f1	count(f1)
+1	2
+2	1
+drop table t1;

mysql-test/t/user_var.test

@@ -222,3 +222,11 @@ drop table t1,t2;
 insert into city 'blah';
 SHOW COUNT(*) WARNINGS;
 SHOW COUNT(*) ERRORS;
+
+#
+# Bug#28494: Grouping by Item_func_set_user_var produces incorrect result.
+#
+create table t1(f1 int);
+insert into t1 values(1),(1),(2);
+select @a:=f1, count(f1) from t1 group by 1;
+drop table t1;

sql/item_func.cc

@@ -4290,9 +4290,11 @@ void Item_func_set_user_var::make_field(Send_field *tmp_field)
     TRUE        Error
 */
 
-int Item_func_set_user_var::save_in_field(Field *field, bool no_conversions)
+int Item_func_set_user_var::save_in_field(Field *field, bool no_conversions,
+                                          bool can_use_result_field)
 {
-  bool use_result_field= (result_field && result_field != field);
+  bool use_result_field= (!can_use_result_field ? 0 :
+                          (result_field && result_field != field));
   int error;
 
   /* Update the value of the user variable */

sql/item_func.h

@@ -1220,7 +1220,13 @@ class Item_func_set_user_var :public Item_func
   void print(String *str);
   void print_as_stmt(String *str);
   const char *func_name() const { return "set_user_var"; }
-  int save_in_field(Field *field, bool no_conversions);
+  int save_in_field(Field *field, bool no_conversions,
+                    bool can_use_result_field);
+  int save_in_field(Field *field, bool no_conversions)
+  {
+    return save_in_field(field, no_conversions, 1);
+  }
+  void save_org_in_field(Field *field) { (void)save_in_field(field, 1, 0); }
 };