sql server 2005 '更新自'询问 [英] sql server 2005 'update from' query
问题描述
我正在尝试根据另一个表中的用户 ID 更新一个表.我从语法中遇到了更新，但我正在努力正确编写我的查询.
I'm trying to update a table based upon the user id from another table. I've come across the Update from syntax but I'm struggling to write my query correctly.
下面的代码应该向您展示我正在尝试做什么.当我运行它时，我得到 0 行影响.
The below code should show you what I'm attempting to do. When i run it i get 0 rows affected.
update jared_test
set user_count = 1
from new_user nuj
inner join (select us.userID
from users us
where us.email = 'j@j.co.uk') u on nuj.userid = u.userid
/********编辑*******************\
/********EDIT*******************\
我发现我的 Cursor 循环存在问题，导致它无法正常工作，因此这确实有效.但是，如果在这种情况下 where 比 from 更好进行优化，我会很感兴趣.
I discovered there was a problem with my Cursor loop that was preventing this from working, so this does actually work. However I'd be interested if a where is better than a from in this instance for optimisations.
推荐答案
我不是 100% 解释为什么其他解决方案使用子选择，它的执行速度通常比常规连接慢.虽然 taos subselect 本质上是一个普通的 join，只是写的很有趣.
I'm not 100% on why the other solutions are using a subselect which will perform slower than a regular join most often. Though taos subselect is essentially a regular join just written interestingly.
update aliasName
set aliasName.user_count =1
from new_user aliasName
inner join users u on aliasName.userid = u.userid
where email = 'j@j.co.uk'
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