after review fixes:

 allowed parsing of table fields inside aggregate functions
 added new tests of fields resolving in grouping


mysql-test/r/func_gconcat.result:
  allowed parsing of table fields inside aggregate functions
mysql-test/r/subselect.result:
  added new tests of fields resolving in grouping
mysql-test/t/func_gconcat.test:
  allowed parsing of table fields inside aggregate functions
mysql-test/t/subselect.test:
  added new tests of fields resolving in grouping
sql/item_subselect.cc:
  allowed parsing of table fields inside aggregate functions

mysql-test/r/func_gconcat.result

@@ -285,6 +285,15 @@ insert into t2 values (1, 5), (2, 4), (3, 3), (3,3);
 select group_concat(c) from t1;
 group_concat(c)
 2,3,4,5
+select group_concat(c order by (select c from t2 where t2.a=t1.a limit 1)) as grp from t1;
+grp
+5,4,3,2
+select group_concat(c order by (select mid(group_concat(c order by a),1,5) from t2 where t2.a=t1.a)) as grp from t1;
+grp
+5,4,3,2
+select group_concat(c order by (select mid(group_concat(c order by a),1,5) from t2 where t2.a=t1.a) desc) as grp from t1;
+grp
+2,4,3,5
 select t1.a, group_concat(c order by (select c from t2 where t2.a=t1.a limit 1)) as grp from t1 group by 1;
 a	grp
 1	2

mysql-test/r/subselect.result

@@ -1954,4 +1954,12 @@ howmanyvalues	mycount
 2	2
 3	3
 4	4
+SELECT a.howmanyvalues, (SELECT count(*) from t1 b where b.howmanyvalues = a.howmanyvalues) as mycount from t1 a group by a.howmanyvalues;
+howmanyvalues	mycount
+1	1
+2	2
+3	3
+4	4
+SELECT a.howmanyvalues, (SELECT count(*) from t1 b where b.howmanyvalues = a.avalue) as mycount from t1 a group by a.howmanyvalues;
+ERROR 42S22: Unknown column 'a.avalue' in 'where clause'
 drop table t1;

mysql-test/t/func_gconcat.test

@@ -168,8 +168,10 @@ insert into t1 values (1, 2), (2, 3), (2, 4), (3, 5);
 create table t2 (a int, c int);
 insert into t2 values (1, 5), (2, 4), (3, 3), (3,3);
 select group_concat(c) from t1;
+select group_concat(c order by (select c from t2 where t2.a=t1.a limit 1)) as grp from t1;
+select group_concat(c order by (select mid(group_concat(c order by a),1,5) from t2 where t2.a=t1.a)) as grp from t1;
+select group_concat(c order by (select mid(group_concat(c order by a),1,5) from t2 where t2.a=t1.a) desc) as grp from t1;
 select t1.a, group_concat(c order by (select c from t2 where t2.a=t1.a limit 1)) as grp from t1 group by 1;
-
 select t1.a, group_concat(c order by (select mid(group_concat(c order by a),1,5) from t2 where t2.a=t1.a)) as grp from t1 group by 1;
 select t1.a, group_concat(c order by (select mid(group_concat(c order by a),1,5) from t2 where t2.a=t1.a) desc) as grp from t1 group by 1;
 

mysql-test/t/subselect.test

@@ -1259,4 +1259,7 @@ SELECT howmanyvalues, count(*) from t1 group by howmanyvalues;
 SELECT a.howmanyvalues, (SELECT count(*) from t1 b where b.howmanyvalues = a.howmanyvalues) as mycount from t1 a group by a.howmanyvalues;
 CREATE INDEX t1_howmanyvalues_idx ON t1 (howmanyvalues);
 SELECT a.howmanyvalues, (SELECT count(*) from t1 b where b.howmanyvalues+1 = a.howmanyvalues+1) as mycount from t1 a group by a.howmanyvalues;
+SELECT a.howmanyvalues, (SELECT count(*) from t1 b where b.howmanyvalues = a.howmanyvalues) as mycount from t1 a group by a.howmanyvalues;
+-- error 1054
+SELECT a.howmanyvalues, (SELECT count(*) from t1 b where b.howmanyvalues = a.avalue) as mycount from t1 a group by a.howmanyvalues;
 drop table t1;

sql/item_subselect.cc

@@ -70,7 +70,14 @@ void Item_subselect::init(st_select_lex *select_lex,
   }
   else
   {
-    parsing_place= unit->outer_select()->parsing_place;
+    SELECT_LEX *outer_select= unit->outer_select();
+    /*
+      do not take into account expression inside aggregate functions because
+      they can access original table fields
+    */
+    parsing_place= (outer_select->in_sum_expr ?
+                    NO_MATTER :
+                    outer_select->parsing_place);
     if (select_lex->next_select())
       engine= new subselect_union_engine(unit, result, this);
     else