Question

SELECT * FROM (
                SELECT qid,via,date,uid, via as cool FROM questions WHERE via != '' AND (uid = 3 OR `uid` IN (SELECT uid_followed FROM followers WHERE uid_follower =  3 AND unfollowed = 0))
                AND via NOT IN (SELECT qid FROM votes WHERE uid =  3)
                UNION ALL
                SELECT qid,via,date,uid, qid as cool FROM questions WHERE via = '' AND (uid = 3 OR `uid` IN (SELECT uid_followed FROM followers WHERE uid_follower =  3 AND unfollowed = 0))
                AND qid NOT IN (SELECT qid FROM votes WHERE uid =  3)
                ) as a
                GROUP BY cool
                ORDER BY date DESC

这需要3秒多的时间，我已将索引放在列qid和via上的正确列中。复杂性是我想要一个独特的qid，并且有些行有qid但是通过via字段实际上是超链接到其他qids。并且qid最多没有uid = 3（userID 3）的投票条目另外，它必须按时间顺序排序。

Answer 1

试试这个：

SELECT qid,via,date,uid,
case
    when via = '' then qid
    else via
end as cool
FROM questions
WHERE (via != ''
AND via NOT IN (SELECT qid FROM votes WHERE uid =  3)
OR via = ''
AND qid NOT IN (SELECT qid FROM votes WHERE uid =  3))
AND (uid = 3 OR `uid` IN (SELECT uid_followed FROM followers WHERE uid_follower =  3 AND unfollowed = 0))
ORDER BY date DESC

没有UNION ALL和GROUP BY

告诉我它是否正常。我使用OR逻辑运算符压缩了两个查询。

您不必关心via字段的NULL值。我使用你的符号（！=''或=''），但也许你会考虑NULL值。

优化这个mysql查询GROUP BY + ORDER BY + UNION ALL

1 个答案: