How to Efficiently Retrieve the Last Row for Each Group in MySQL?

select *
    from foo as a
    where a.id = (select max(id) from foo where uid = a.uid group by uid)
    group by uid;

SELECT t1.* FROM foo t1
  JOIN (SELECT uid, MAX(id) id FROM foo GROUP BY uid) t2
    ON t1.id = t2.id AND t1.uid = t2.uid;

SELECT t1.* FROM foo t1
  LEFT JOIN foo t2
    ON t1.id < t2.id AND t1.uid = t2.uid
WHERE t2.id is NULL;

CREATE TABLE foo (
    id INT(10) NOT NULL AUTO_INCREMENT,
    uid INT(10) NOT NULL,
    value VARCHAR(50) NOT NULL,
    PRIMARY KEY (`id`),
    INDEX `uid` (`uid`)
);

id, uid, value
1,   1, hello
2,   2, cheese
3,   2, pickle
4,   1, world

id, uid, value
3,   2, pickle
4,   1, world