Mysql子查询很慢

Question

我有这个 MySQL 问题。它工作正常，但速度非常慢。运行最多需要 30 秒。

SELECT t.Id, Subject, k.info
FROM tip t
LEFT JOIN comments k ON t.Id = k.Tipid
WHERE event = 1
AND k.Id
IN (
SELECT Max(Id) FROM comments GROUP BY Tipid
)

如果我只运行子查询(SELECT Max(Id) FROM comments GROUP BY Tipid)，运行大约需要 0.02 秒。

子查询有问题。你有什么想法吗？

Answer 1

如果你选择 max(id) 就不需要 group by 试试这个

    SELECT t.Id, Subject, k.info
    FROM tip t
    LEFT JOIN comments k ON t.Id = k.Tipid
    WHERE event = 1
    AND k.Id in (select Max(Id) from comments)