Fixed LP bug #776274,

The bug was introduced by the patch that fixed bug 717577.

mysql-test/r/select.result

@@ -5018,3 +5018,16 @@ WHERE t7.f71>0;
 f23
 DROP TABLE t1,t2,t3,t4,t5,t6,t7;
 End of 5.1 tests
+#
+# BUG#776274: substitution of a single row table
+#                    
+CREATE TABLE t1 (a int NOT NULL , b int);
+INSERT INTO t1 VALUES (2,2);
+SELECT * FROM t1 WHERE a = b;
+a	b
+2	2
+EXPLAIN
+SELECT * FROM t1 WHERE a = b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+DROP TABLE t1;

mysql-test/r/select_jcl6.result

@@ -5025,6 +5025,19 @@ WHERE t7.f71>0;
 f23
 DROP TABLE t1,t2,t3,t4,t5,t6,t7;
 End of 5.1 tests
+#
+# BUG#776274: substitution of a single row table
+#                    
+CREATE TABLE t1 (a int NOT NULL , b int);
+INSERT INTO t1 VALUES (2,2);
+SELECT * FROM t1 WHERE a = b;
+a	b
+2	2
+EXPLAIN
+SELECT * FROM t1 WHERE a = b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+DROP TABLE t1;
 set join_cache_level=default;
 show variables like 'join_cache_level';
 Variable_name	Value

mysql-test/r/select_pkeycache.result

@@ -5018,3 +5018,16 @@ WHERE t7.f71>0;
 f23
 DROP TABLE t1,t2,t3,t4,t5,t6,t7;
 End of 5.1 tests
+#
+# BUG#776274: substitution of a single row table
+#                    
+CREATE TABLE t1 (a int NOT NULL , b int);
+INSERT INTO t1 VALUES (2,2);
+SELECT * FROM t1 WHERE a = b;
+a	b
+2	2
+EXPLAIN
+SELECT * FROM t1 WHERE a = b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+DROP TABLE t1;

mysql-test/t/select.test

@@ -4211,3 +4211,17 @@ SELECT t2.f23 FROM
 DROP TABLE t1,t2,t3,t4,t5,t6,t7;
 
 --echo End of 5.1 tests
+
+--echo #
+--echo # BUG#776274: substitution of a single row table
+--echo #                    
+
+CREATE TABLE t1 (a int NOT NULL , b int);
+INSERT INTO t1 VALUES (2,2);
+
+SELECT * FROM t1 WHERE a = b;
+EXPLAIN
+SELECT * FROM t1 WHERE a = b;
+
+DROP TABLE t1;
+

sql/item_cmpfunc.cc

@@ -5740,18 +5740,19 @@ void Item_equal::update_const()
   List_iterator<Item> it(equal_items);
   if (with_const)
     it++;
-  Item *item= it++;
-  while (item)
+  Item *item;
+  while ((item= it++))
   {
     if (item->const_item())
     {
-      it.remove();
-      Item *next_item= it++;
-      add_const(item);
-      item= next_item;
-    }
-    else
-      item= it++;
+      if (item == equal_items.head())
+        with_const= TRUE;
+      else
+      {
+        it.remove();
+        add_const(item);
+      }
+    } 
   }
 }