我需要更新一个表,但为了获取新值,我似乎需要创建一个临时表。原因是我需要计算 max
的 sum
。我能做到吗?
伪代码如下所示:
UPDATE users u SET usersContribution = [CREATE TEMPORARY TABLE IF NOT EXISTS tmpTbl3 AS
(SELECT ROUND(max(zz.zachetTimestamp - d.answerDate)) as answerDateDiff
FROM zachet zz
JOIN discussionansw d ON d.zachetid=zz.zachetId and d.usersid=zz.usersId and
zz.zachetTimestamp > d.answerDate
WHERE zz.whoTalk=u.userid and
NOT EXISTS (SELECT * FROM discussionansw
WHERE zachetid=zz.zachetId and usersid=u.userid')
GROUP BY zz.zachetId)]
SELECT SUM(answerDateDiff) FROM tmpTbl3;"
我使用括号来显示必须完成的部分,但被 UPDATE 查询忽略...
我有 max
和 sum
,但我没有找到避免 tmp 表的方法。但如果可以的话,我们会很高兴能有这样的解决方案。
我把答案放在这里,这是我在@flaschenpost和这篇文章的帮助下得到的:SQL Update to the SUM of its joined values
CREATE TEMPORARY TABLE IF NOT EXISTS t0tmpTbl3 AS
(SELECT zz.whoTalk, ROUND(max(zz.zachetTimestamp - d.answerDate)) as answerDateDiff
FROM zachet zz
JOIN discussionansw d ON d.zachetid=zz.zachetId and d.usersid=zz.usersId and
zz.zachetTimestamp > d.answerDate
WHERE
NOT EXISTS (SELECT * FROM discussionansw WHERE zachetid=zz.zachetId and usersid=zz.whoTalk)
GROUP BY zz.zachetId);
UPDATE users u
JOIN (SELECT whoTalk, SUM(answerDateDiff) sumAnswerDateDiff
FROM t0tmpTbl3 GROUP BY whoTalk) t
ON u.usersId=t.whoTalk
SET u.usersContribution=sumAnswerDateDiff;
最佳答案
你能把它分成两个查询吗?
drop temporary table if exists tmp_maxsumofsomething;
create temporary table tmp_maxsumofsomething
select max(), sum(), ...
from zachet z inner join discussionansw a on ...
group by...
;
update u inner join tmp_maxsumofsomething t on ... set u.... = t...
临时表仅在创建它们的连接中可见,因此具有线程安全性。
编辑:只要您的查询有意义,您就可以尝试:
DROP TEMPORARY TABLE IF EXISTS tmpTbl3;
CREATE TEMPORARY TABLE tmpTbl3
SELECT zz.whoTalk as userId, ROUND(max(zz.zachetTimestamp - d.answerDate)) as answerDateDiff
FROM zachet zz, discussionansw d
WHERE d.zachetid=zz.zachetId
and d.usersid=zz.usersId and zz.zachetTimestamp > d.answerDate
# What do you mean ? by:
# and (SELECT count(*) FROM discussionansw
# WHERE zachetid=zz.zachetId and usersid=u.userid) = 0
# Think about a reasonable WHERE NOT EXISTS clause!
GROUP BY zz.whoTalk
然后你就有了要加入的临时表:
update users u
inner join tmpTbl3 tm on u.userId = tm.userId
set u.usersContribution = tm.answerDateDiff
如果您有足够的勇气编写需要这些查询的应用程序,那么您不应该害怕学习更多 SQL 和 MySQL 的一些概念。您来这里是为了探索概念,而不是免费雇用程序员。
关于mysql - 将 MySQL 表更新为构造的双聚合,这取决于表本身,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23434552/