求简单SQL

[fength2004]

有两张表A1,A2, 其中M,N 为表的项目, M为主键
表A1 表A2
M N M N
___________ _______
a 1 a 2
b 11 c 22

求用SQL文实现如下结果
M A1.N A2.N
___________________________
a 1 2
b 11 null
c null 22

[xiaoxiao1984]

select A1.M, A1.N, A2.N from A1 left join A2 on A1.M = A2.M
union all
select A2.M, null, A2.N from A2 where not exists(select 1 from A1 where A1.M = A2.M)

[chinacomstar]

select A1.M,A1.N,B1.M,B1.N from A1 LEFT JOIN B1 ON A1.M=B1.M
union
select A1.M,A1.N,B1.M,B1.N from A1 RIGHT JOIN B1 ON ON A1.M=B1.M
如果还想多一点判断，还可以在Column前面加iif的判断，比如为空就置0
比如iif(A1.N is null,0,A1.N)
这样可以吗，可以的话要记得给分哦，hoho

[wiler]

偶也要分分，hoho
select A1.M, A1.N, A2.N from A1 ,A2
where A1.M = A2.M(+)
union
select A2.M, A1.N, A2.N from A1 ,A2
where A1.M(+) = A2.M

[fength2004]

都是高人啊, 谢了,