我有以下两张桌子:
Codes
Code key1 key2
1 a hh
2 a
3 a
4 a
Orders
key1 key2 val1
a aa foo
h hh bar
我想得到
Desired output
code key1 key2 val1
1 a hh bar
2 a
3 a
4 a
我试过用内部连接命令:
select
ordersa.key2,
code,
ordersb.date
from
order ordersa
right join codes
on codes.key1 = orders.key1
inner join orders ordersb
on codes.key2 = ordersb.key2
但这会去掉key2列中的所有空数据,我得到:
code key1 key2 val1
1 a hh bar
对我如何做到这点有什么建议吗?
最佳答案
SELECT
c.Code,
c.key1,
IFNULL(c.key2, '') key2,
IFNULL(o.val1, '') val1,
FROM Codes c
LEFT JOIN Orders o ON c.key2 = o.key2
关于mysql - MySQL多表联接为空,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/54471533/