Question

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;
)

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?

Thanks,

Chris.

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

results:

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

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

Answer 1

Try this query –

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;

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;