Fix for BUG#11821 manually merged

sql/item.cc:
  Auto merged

mysql-test/r/subselect.result

@@ -2837,3 +2837,9 @@ WHERE select_id = 0 OR select_id = 1);
 values_id
 1
 DROP TABLE t1, t2;
+create table t1 (fld enum('0','1'));
+insert into t1 values ('1');
+select * from (select max(fld) from t1) as foo;
+max(fld)
+1
+drop table t1;

mysql-test/t/subselect.test

@@ -1859,3 +1859,11 @@ WHERE values_id IN (SELECT values_id FROM t2
                     WHERE select_id = 0 OR select_id = 1);
 
 DROP TABLE t1, t2;
+
+# BUG#11821 : Select from subselect using aggregate function on an enum
+# segfaults:
+create table t1 (fld enum('0','1'));
+insert into t1 values ('1');
+select * from (select max(fld) from t1) as foo;
+drop table t1;
+

sql/item.cc

@@ -5421,9 +5421,13 @@ void Item_type_holder::get_full_info(Item *item)
   if (fld_type == MYSQL_TYPE_ENUM ||
       fld_type == MYSQL_TYPE_SET)
   {
+    if (item->type() == Item::SUM_FUNC_ITEM &&
+        (((Item_sum*)item)->sum_func() == Item_sum::MAX_FUNC ||
+         ((Item_sum*)item)->sum_func() == Item_sum::MIN_FUNC))
+      item = ((Item_sum*)item)->args[0];
     /*
-      We can have enum/set type after merging only if we have one enum/set
-      field and number of NULL fields
+      We can have enum/set type after merging only if we have one enum|set
+      field (or MIN|MAX(enum|set field)) and number of NULL fields
     */
     DBUG_ASSERT((enum_set_typelib &&
                  get_real_type(item) == MYSQL_TYPE_NULL) ||