Fix for bug #8164: subquery with INFORMATION_SCHEMA.COLUMNS, 100 % CPU

mysql-test/r/information_schema.result

@@ -631,3 +631,10 @@ TABLES	UPDATE_TIME	datetime
 TABLES	CHECK_TIME	datetime
 ROUTINES	CREATED	datetime
 ROUTINES	LAST_ALTERED	datetime
+SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES A
+WHERE NOT EXISTS 
+(SELECT * FROM INFORMATION_SCHEMA.COLUMNS B
+WHERE A.TABLE_SCHEMA = B.TABLE_SCHEMA
+AND A.TABLE_NAME = B.TABLE_NAME);
+COUNT(*)
+0

mysql-test/t/information_schema.test

@@ -400,3 +400,12 @@ information_schema.columns
 where data_type = 'longtext';
 select table_name, column_name, data_type from information_schema.columns
 where data_type = 'datetime';
+
+#
+# Bug #8164  subquery with INFORMATION_SCHEMA.COLUMNS, 100 % CPU
+#
+SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES A
+WHERE NOT EXISTS 
+(SELECT * FROM INFORMATION_SCHEMA.COLUMNS B
+  WHERE A.TABLE_SCHEMA = B.TABLE_SCHEMA
+  AND A.TABLE_NAME = B.TABLE_NAME);

sql/sql_show.cc

@@ -1649,6 +1649,10 @@ bool uses_only_table_name_fields(Item *item, TABLE_LIST *table)
                                strlen(item_field->field_name), 0)))
       return 0;
   }
+  if (item->type() == Item::SUBSELECT_ITEM &&
+      !item->const_item())
+    return 0;
+
   return 1;
 }