MySQL - 按DESC的顺序分组

Question

table:uuid,version,datetime

版本不是唯一的,但想法是仅获取给定uuid的最新日期时间的行

SELECT * FROM table WHERE uuid='bla' GROUP BY version ORDER BY datetime desc

...当然获取datetime asc结果 - 有没有办法将该组"预先排序"到desc,以便只获取最新版本？

Answer 1

由于该表只有那3个字段,并且您通过uid进行过滤,因此您只需使用不带JOIN的MAX:

SELECT version, MAX(datetime) Maxdatetime
FROM table
WHERE uuid='bla'
GROUP BY version

但是,如果表中有更多字段,或者您没有过滤uid- 您需要先为每个版本获取MAX日期时间,然后选择行:

SELECT t.uuid, t.version, t.datetime 
FROM table t JOIN (
    SELECT version, MAX(datetime) Maxdatetime
    FROM table
    WHERE uuid='bla'
    GROUP BY version
) r ON t.version = r.version AND t.datetime = r.Maxdatetime
WHERE t.uuid='bla'
ORDER BY t.datetime desc

Answer 2

SELECT * FROM 
(SELECT * FROM table WHERE uuid='bla' ORDER BY datetime desc) table 
GROUP BY version;