mysql order by field

CREATE TABLE `foo` (
  `bar` INT(3),
  KEY `bar` (`bar`)
) ENGINE=MyISAM;

INSERT INTO `foo` VALUES (12), (57), (33), (7), (101);

SELECT `bar`
FROM foo
WHERE bar IN (101, 7, 12, 57)
ORDER BY FIELD(bar, 101, 7, 12, 57);

/*
+------+
| bar  |
+------+
|  101 |
|    7 |
|   12 |
|   57 |
+------+
4 rows in set (0.00 sec)
*/