MDEV-29988 group by fix

mysql-test/main/func_group.result

-drop table if exists t1,t2,t3,t4,t5,t6;
 set @sav_dpi= @@div_precision_increment;
 set div_precision_increment= 5;
 show variables like 'div_precision_increment';
@@ -2566,5 +2565,15 @@ stddev_samp(i)	stddev_pop(i)	stddev(i)	std(i)
 drop view v1;
 drop table t1;
 #
+# MDEV-29988: Major performance regression with 10.6.11
+#
+create table t1 (a varchar(10) charset utf8mb4, b int, c int);
+insert t1 values (1,2,3),(4,5,6),(1,7,8);
+select concat(a,":",group_concat(b)) from t1 group by a;
+concat(a,":",group_concat(b))
+1:2,7
+4:5
+drop table t1;
+#
 # End of 10.3 tests
 #

mysql-test/main/func_group.test

@@ -2,10 +2,6 @@
 # simple test of all group functions
 #
 
---disable_warnings
-drop table if exists t1,t2,t3,t4,t5,t6;
---enable_warnings
-
 set @sav_dpi= @@div_precision_increment;
 set div_precision_increment= 5;
 show variables like 'div_precision_increment';
@@ -1800,6 +1796,14 @@ select * from v1;
 drop view v1;
 drop table t1;
 
+--echo #
+--echo # MDEV-29988: Major performance regression with 10.6.11
+--echo #
+create table t1 (a varchar(10) charset utf8mb4, b int, c int);
+insert t1 values (1,2,3),(4,5,6),(1,7,8);
+select concat(a,":",group_concat(b)) from t1 group by a;
+drop table t1;
+
 --echo #
 --echo # End of 10.3 tests
 --echo #

sql/item.h

@@ -6976,6 +6976,11 @@ class Item_direct_ref_to_item : public Item_direct_ref
   bool is_expensive() { return m_item->is_expensive(); }
   Item* build_clone(THD *thd) { return get_copy(thd); }
 
+  void split_sum_func(THD *thd, Ref_ptr_array ref_pointer_array,
+                      List<Item> &fields, uint flags)
+  {
+    m_item->split_sum_func(thd, ref_pointer_array, fields, flags);
+  }
   /*
     This processor states that this is safe for virtual columns
     (because this Item transparency)