php - PHP & MySQL check mysql left join with specified condition

Question

I'm using xenforo, that has tables:

• user: user_id, user_group_id
• thread: thread_id, user_id, sticky

I need a query to change user_group_id from 15 to 14 if they dont have any stick thread (sticky=0 in thread).

Is this possible with a left join, and if so how?

Thanks.

Answer 1

update user u
set u.user_group_id=14
where u.user_group_id=15 and
  (select sticky from thread where thread_id = u.user_id)=0;

Answer 2

你的意思是：

UPDATE user SET user_group_id=14 WHERE user_group_id=15 AND 
0 = (SELECT COUNT(*) FROM thread WHERE sticky=0 AND user_id=user.user_id)

这不使用左连接。必须使用 LEFT JOIN 吗？

Answer 3

这会做到的

update user set user_group_id = 14 
where user_group_id = 15 
and user_id in (select user_id from threads where sticky=0)

编辑：

在这种情况下，您可以在更新时加入两个表，而不是使用子查询，如下所示

update user u
inner join thread t on
    u.user_id = t.user_id and t.sticky = 0
set u.user_group_id = 14
where u.user_group_id = 15

在此处查看演示 sqlfiddle http://sqlfiddle.com/#!2/58b121/1。