Fixed LP bug #798621.

The patch for bugs 717577 and 724942 has missed to make adjustments for the
call item_equal->add_const(const_item, orig_field_item) in the function
check_simple_equality that builds multiple equality for a field and a constant.
As a result, when this field happens to be a view field and the corresponding
Item_field object F is wrapped in an Item_direct_view_ref object R the object
F is placed in the multiple equality instead of the object R.
A substitution of an equal item for F potentially can cause very serious
problems and in some cases can lead to crashes of the server.

mysql-test/r/view.result

@@ -4184,3 +4184,26 @@ DELETE FROM v3;
 ERROR HY000: The target table v3 of the DELETE is not updatable
 DROP VIEW v1,v2,v3;
 DROP TABLE t1;
+#
+# Bug#798621: crash with a view string field equal  
+#             to a constant
+#
+CREATE TABLE t1 (a varchar(32), b int) ;
+INSERT INTO t1 VALUES ('j', NULL), ('c', 8), ('c', 1);
+CREATE VIEW v1 AS SELECT * FROM t1;
+CREATE TABLE t2 (a varchar(32)) ;
+INSERT INTO t2 VALUES ('j'), ('c');
+SELECT * FROM v1 LEFT JOIN t2 ON t2.a = v1.a 
+WHERE v1.b = 1 OR v1.a = 'a' AND LENGTH(v1.a) >= v1.b;
+a	b	a
+c	1	c
+EXPLAIN EXTENDED
+SELECT * FROM v1 LEFT JOIN t2 ON t2.a = v1.a 
+WHERE v1.b = 1 OR v1.a = 'a' AND LENGTH(v1.a) >= v1.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a` from `test`.`t1` left join `test`.`t2` on((`test`.`t2`.`a` = `test`.`t1`.`a`)) where ((`test`.`t1`.`b` = 1) or ((`test`.`t1`.`a` = 'a') and (length(`test`.`t1`.`a`) >= `test`.`t1`.`b`)))
+DROP VIEW v1;
+DROP TABLE t1,t2;

mysql-test/t/view.test

@@ -4134,3 +4134,24 @@ DELETE FROM v3;
 
 DROP VIEW v1,v2,v3;
 DROP TABLE t1;
+
+--echo #
+--echo # Bug#798621: crash with a view string field equal  
+--echo #             to a constant
+--echo #
+
+CREATE TABLE t1 (a varchar(32), b int) ;
+INSERT INTO t1 VALUES ('j', NULL), ('c', 8), ('c', 1);
+CREATE VIEW v1 AS SELECT * FROM t1;
+
+CREATE TABLE t2 (a varchar(32)) ;
+INSERT INTO t2 VALUES ('j'), ('c');
+
+SELECT * FROM v1 LEFT JOIN t2 ON t2.a = v1.a 
+  WHERE v1.b = 1 OR v1.a = 'a' AND LENGTH(v1.a) >= v1.b;
+EXPLAIN EXTENDED
+SELECT * FROM v1 LEFT JOIN t2 ON t2.a = v1.a 
+  WHERE v1.b = 1 OR v1.a = 'a' AND LENGTH(v1.a) >= v1.b;
+
+DROP VIEW v1;
+DROP TABLE t1,t2;

sql/sql_select.cc

@@ -10334,7 +10334,7 @@ static bool check_simple_equality(Item *left_item, Item *right_item,
         !((Item_field*)left_item)->get_depended_from() &&
         right_item->const_item() && !right_item->is_expensive())
     {
-      orig_field_item= left_item;
+      orig_field_item= orig_left_item;
       field_item= (Item_field *) left_item;
       const_item= right_item;
     }
@@ -10342,7 +10342,7 @@ static bool check_simple_equality(Item *left_item, Item *right_item,
              !((Item_field*)right_item)->get_depended_from() &&
              left_item->const_item() && !left_item->is_expensive())
     {
-      orig_field_item= right_item;
+      orig_field_item= orig_right_item;
       field_item= (Item_field *) right_item;
       const_item= left_item;
     }