在MySQL中返回每个'group by'的'last'行 [英] Returning the 'last' row of each 'group by' in MySQL

问题描述

有没有更有效的方式来做以下事情？

Is there a more efficient way of doing the following?

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，但是这个答案是这样做的最好方法 - 如何选择第一行对于MySQL中的每个组？

This answer looks similar, but is this answer the best way of doing this - How to select the first row for each group in MySQL?

谢谢，

Chris。

PS该表看起来像：

P.S. the table looks like:

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`)
)

data：

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

结果：

results:

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

请参阅 http：// www。 barricane.com/2012/02/08/mysql-select-last-matching-row.html 以获取更多详情。

See http://www.barricane.com/2012/02/08/mysql-select-last-matching-row.html for more details.

推荐答案

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 来分析查询。

---

Then use EXPLAIN to analyze queries.

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

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