在MySQL中返回每个“ group by”的“ last”行

Question

有没有更有效的方法来执行以下操作？

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

这个答案看起来很相似，但这是这样做的最好方法-
如何在MySQL中为每个组选择第一行？

谢谢，

克里斯。

PS表看起来像：

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`)
)

数据：

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

结果：

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

有关更多详细信息，请参见http://www.barricane.com/2012/02/08/mysql-select-last-matching-
row.html
。

Answer 1

试试这个查询-

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;

然后使用EXPLAIN分析查询。

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