如何选择某个用户未加入Mysql的组? [英] How to select the groups which a certain user doesn't join with Mysql?

问题描述

给出三个数据表theUser，theGroup，membership:

theUser:(*user_id*, username),
theGroup:(*group_id*, groupname),
membership:(*group_id*, *user_id*)

例如，组2具有用户007和008，membership应该类似于:

For instance, group 2 has user 007 and 008, the membership should be like:

group_id      user_id
2             007
2             008

现在，我希望选择用户008尚未加入的组.你能告诉我怎么做吗?提前致谢！

Now I wish to select the groups that user 008 HAS NOT BEEN IN. Could you tell me how to do that? Thanks in advance!

推荐答案

几种不同的方法可以做到这一点.这是带有outer join / null支票的:

Several different ways to do this. Here's one with an outer join / null check:

select g.*
from thegroup g
   left join membership m on g.groupid = m.groupid and m.userid = '008'
where m.groupid is null

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