现在有如下的表:tb_item
ItemID userID targetID other
1 1 2 aaab
2 2 1 bbc
3 null null kkkk表tb_userUserID Name
1 SSS
2 MMM需要通过SQL语句显示如下内容:
ItemID userName targetName other
1 SSS MMM aaab
2 MMM SSS bbc
3 null null kkkk
应当如何做?我主要是不懂第三记录当外键为空时如何解决?
ItemID userID targetID other
1 1 2 aaab
2 2 1 bbc
3 null null kkkk表tb_userUserID Name
1 SSS
2 MMM需要通过SQL语句显示如下内容:
ItemID userName targetName other
1 SSS MMM aaab
2 MMM SSS bbc
3 null null kkkk
应当如何做?我主要是不懂第三记录当外键为空时如何解决?
from tb_item as left join tb_user as b on a.UserID=b.UserID
left join tb_user as c on a.UserID=c.UserID
insert @a select
1, 1, 2, 'aaab'
union all select 2, 2, 1, 'bbc'
union all select 3, null, null, 'kkkk'declare @b table(UserID int, Name varchar(10))
insert @b select 1 ,'SSS'
union all select 2 ,'MMM'
select itemid,b.name username,c.name targetname,other from @a a left join @b b on a.userid=b.userid left join @b c on a.targetid=c.userid
select a.itemid,b.name,c.name,a.other from tb_item as a
left join
tb_user as b
on a.userid = b.userid
left join
tb_user as c
on a.targetid = c.userid