如何获取另一个表字段信息

Question

我有三个表，user / team / user_team（多对多）

user
-----------
id  name 
1   Tom
2   Jerry
3   John

team
------------
id   name
1    t1
2    t2
3    t3

user_team
---------------------
userid   teamid  isdeleted
1        t1       0   <----(0 means not deleted record, which can be searched out)
2        t2       1   <----(1 means deleted record, which can not be searched out)

我希望获得所有团队记录信息以及相关的用户信息，如下所示

--------------
tid tname  username
1   t1     Tom
2   t2     
3   t3

你能告诉我如何编写sql语句吗？

抱歉我的错误。我通过在团队表中再添加一条记录t3来更新我的问题。

Answer 1

试一试。在这里查看演示小提琴http://sqlfiddle.com/#!2/d918a/2

select t.id as tid,
t.name as tname,
case when ut.isdeleted = 0 then u.name else '' end as username
from team t 
left join user_team ut
on t.name = ut.teamid
left join user u
on ut.userid = u.id;

这将导致

Answer 2

试试这个：

         SELECT t.id tid, t.name tname, GROUP_CONCAT(u.name) usernames
           FROM user_team ut 
LEFT OUTER JOIN team t ON ut.teamid = t.id
LEFT OUTER JOIN user u ON ut.userid = u.id
       GROUP BY t.id;

要包含可以搜索到的标志，请尝试此操作（仅包含标志条件）：

         SELECT t.id tid, t.name tname, GROUP_CONCAT(u.name) usernames
           FROM user_team ut 
LEFT OUTER JOIN team t ON ut.teamid = t.id
LEFT OUTER JOIN user u ON ut.userid = u.id
            AND ut.isdeleted = 1 --this will add a condition for deleted teams
       GROUP BY t.id;

Answer 3

试试这个：

Select a.id as tid
a.name as tname
b.name as username
from team a
LEFT JOIN user_team c on a.name = c.teamid and c.isdeleted = 0
LEFT JOIN user b on b.id = c.userid

Answer 4

我认为您正在寻找的是一个简单的OUTER JOIN：

select t.id as tid,
    t.name as tname,
    u.name as username
from team t 
    left join user_team ut on t.id = ut.teamid and ut.isdeleted = 0
    left join user u on ut.userid = u.id

A Visual Explanation of SQL Joins