Fixed LP bug #800518.

The function simple_pred did not take into account that a multiple equality
could include ref items (more exactly items of the class Item_direct_view_ref).
It caused crashes for queries over derived tables or views if the
min/max optimization could be applied to these queries.

mysql-test/r/derived.result

@@ -425,3 +425,19 @@ SELECT * FROM (SELECT DISTINCT * FROM t2) t, t1  WHERE t1.a = t.a;
 a	a
 3	3
 DROP TABLE t1,t2;
+#
+#  LP bug #800518: crash with a query over a derived table
+#                  when a min/max optimization is applied
+#
+CREATE TABLE t1 (a int, b int, c varchar(10), INDEX idx(a,b)) ;
+INSERT INTO t1 VALUES 
+(100, 3, 'xxx'), (200, 7, 'yyyyyyy'), (100, 1, 't'),
+(200, 4, 'aaaa'), (100, 3, 'eee'), (100, 5, 'zzzzz');
+EXPLAIN
+SELECT MAX(b) FROM (SELECT * FROM t1) AS t WHERE a = 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+SELECT MAX(b) FROM (SELECT * FROM t1) AS t WHERE a = 100;
+MAX(b)
+5
+DROP TABLE t1;

mysql-test/t/derived.test

@@ -331,3 +331,20 @@ SELECT * FROM (SELECT DISTINCT * FROM t2) t, t1  WHERE t1.a = t.a;
 SELECT * FROM (SELECT DISTINCT * FROM t2) t, t1  WHERE t1.a = t.a;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo #  LP bug #800518: crash with a query over a derived table
+--echo #                  when a min/max optimization is applied
+--echo #
+
+CREATE TABLE t1 (a int, b int, c varchar(10), INDEX idx(a,b)) ;
+INSERT INTO t1 VALUES 
+  (100, 3, 'xxx'), (200, 7, 'yyyyyyy'), (100, 1, 't'),
+  (200, 4, 'aaaa'), (100, 3, 'eee'), (100, 5, 'zzzzz');
+
+EXPLAIN
+SELECT MAX(b) FROM (SELECT * FROM t1) AS t WHERE a = 100;
+SELECT MAX(b) FROM (SELECT * FROM t1) AS t WHERE a = 100;
+
+DROP TABLE t1;
+

sql/opt_sum.cc

@@ -494,11 +494,13 @@ bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
     /* MULT_EQUAL_FUNC */
     {
       Item_equal *item_equal= (Item_equal *) func_item;
+      if (!(args[1]= item_equal->get_const()))
+        return 0;
       Item_equal_fields_iterator it(*item_equal);
-      args[0]= it++;
-      if (it++)
+      if (!(item= it++))
         return 0;
-      if (!(args[1]= item_equal->get_const()))
+      args[0]= item->real_item();
+      if (it++)
         return 0;
     }
     break;