SQL连接查询结果问题

Question

我有两个表，一个是Friends表，另一个表是用户配置表（所有用户相关信息，例如firstname，lastname等）都有它们之间的关系

朋友表（每个用户有两个条目，例如前两行）

现在我想显示上表中的用户名，如下所示

所以在输出中我想删除对我不起作用的重复项 我的查询

select distinct u.FirstName + ' ' + u.LastName As UserName,
      (select distinct  firstname + ' ' + lastname from UserProfiles where id =   uw.friendid) as FriendName
       from UserFriends as uw left join userprofiles as u 
       on u.id = uw.userid 

Answer 1

您需要在UserProfiles上加入UserFriends两次，因为有两列依赖于它。

SELECT  a.ID,
        f.FirstName + ' ' + f.LastName FriendName,
        u.FirstName + ' ' + u.LastName UserName
FROM    UserFriends a
        INNER JOIN UserProfiles f
            ON a.FriendID = f.ID
        INNER JOIN UserProfiles u
            ON a.UserID = u.ID
        INNER JOIN UserFriends dup
            ON a.FriendID = dup.UserID 
                AND dup.FriendID = a.UserID 
                AND a.ID > dup.ID

• SQLFiddle Demo

Answer 2

我建议您必须使用CTE来消除重复项（可以通过自联接表来完成）。我已设法重现您的方案，因此如果您稍微调整一下查询，您将能够获得所需的结果

with cte as
(select 
t1.id as a_id
,t1.friendID as a_friendID
 ,t1.userID as a_userID
,t2.id as b_id
,t2.friendID as b_friendID
,t2.userID as b_userID
 from #temp t1
 left join #user t2 on t1.id+1=t2.id
 ),
 cte2 as

 select 
 a_id
,a_userID
,a_friendID
 from cte t1
 where a_friendID = (select b_friendID from cte t2 where t2.b_id= t1.b_id-1)
 )


select firstname+ ' '+lastname as FriendName
,firstname+ ' '+lastname as UserName 
from cte2 uw
left join   UserProfiles u on uw.a_userID=u.ID and uw.a_friendID=u.id