Question

我有一张表有2张来自同一张表的外键

UserID     Name
1          Alpha
2          Bravo
3          Charlie
4          Delta
5          Foxtrot

Record     UserID     UserID2
1          1          5
2          3
3          4

是否可以将它们显示为多行？

Record      Name
1           Alpha
1           Foxtrot
2           Charlie
3           Delta

我尝试使用INNER JOIN / JOIN但只能使用一个外键（UserID）。

Answer 1

您可以使用两个联接，在这种情况下left join将值放在一行：

select t1.record, t2a.name, t2b.name
from t1 left join
     t2 t2a
     on t2a.userid = t1.userid left join
     t2 t2b
     on t2b.userid = t1.userid2;

对于单独的行，请使用union all：

select t1.record, t2.name
from t1 join
     t2
     on t2.userid = t1.userid
union all
select t1.record, t2.name
from t1 join
     t2
     on t2.userid = t1.userid2
order by record;

Answer 2

更简单的方法：

Select t2.record AS Record,Name
From t1 inner join t2
on t1.userId = t2.UserID or t1.userId = t2.userid2

显示基于两个外键的行

2 个答案: