Fix for bug#18281 group_concat changes charset to binary

 skip charset aggregation for order columns

mysql-test/r/func_gconcat.result

@@ -626,3 +626,8 @@ latin1
 latin1
 drop table t1, t2, t3;
 set names default;
+create table t1 (c1 varchar(10), c2 int);
+select charset(group_concat(c1 order by c2)) from t1;
+charset(group_concat(c1 order by c2))
+latin1
+drop table t1;

mysql-test/t/func_gconcat.test

@@ -414,3 +414,11 @@ select charset(a) from t2;
 select charset(a) from t3;
 drop table t1, t2, t3;
 set names default;
+
+#
+# Bug#18281 group_concat changes charset to binary
+#
+create table t1 (c1 varchar(10), c2 int);
+select charset(group_concat(c1 order by c2)) from t1;
+drop table t1;
+

sql/item_sum.cc

@@ -3226,7 +3226,10 @@ Item_func_group_concat::fix_fields(THD *thd, Item **ref)
   }
 
   if (agg_item_charsets(collation, func_name(),
-                        args, arg_count, MY_COLL_ALLOW_CONV))
+                        args,
+			/* skip charset aggregation for order columns */
+			arg_count - arg_count_order,
+			MY_COLL_ALLOW_CONV))
     return 1;
 
   result.set_charset(collation.collation);