Fix for BUG#11821: Make Item_type_holder be able to work with MIN(field),

  MAX(field).

mysql-test/r/subselect.result

@@ -2721,3 +2721,9 @@ SELECT s.ip, count( e.itemid ) FROM `t1` e JOIN t2 s ON s.sessionid = e.sessioni
 ip	count( e.itemid )
 10.10.10.1	1
 drop tables 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

@@ -1746,3 +1746,11 @@ CREATE TABLE `t2` (
 INSERT INTO `t2` VALUES (1, 1, 1, '10.10.10.1');
 SELECT s.ip, count( e.itemid ) FROM `t1` e JOIN t2 s ON s.sessionid = e.sessionid WHERE e.sessionid = ( SELECT sessionid FROM t2 ORDER BY sessionid DESC LIMIT 1 ) GROUP BY s.ip HAVING count( e.itemid ) >0 LIMIT 0 , 30;
 drop tables 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

@@ -3121,9 +3121,13 @@ 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) ||