mysql> CREATE TABLE IF NOT EXISTS `test` (
    ->   `id` int(11) NOT NULL AUTO_INCREMENT,
    ->   `user_id` bigint(20) NOT NULL,
    ->   PRIMARY KEY (`id`)
    -> ) ENGINE=MyISAM  DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO `test` (`user_id`) VALUES (1),(2),(0),(0);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from `test`;
+----+---------+
| id | user_id |
+----+---------+
|  1 |       1 |
|  2 |       2 |
|  3 |       0 |
|  4 |       0 |
+----+---------+
4 rows in set (0.00 sec)

mysql> select * from `test` where `user_id` = 'test';
+----+---------+
| id | user_id |
+----+---------+
|  3 |       0 |
|  4 |       0 |
+----+---------+
2 rows in set, 1 warning (0.00 sec)