Sql 需要自助加入帮助吗
我有一张桌子XYZ:Sql 需要自助加入帮助吗,sql,sql-server,self-join,Sql,Sql Server,Self Join,我有一张桌子XYZ: ID A B C 1 abc ygh NULL 2 fgfd bjh NULL 3 jhkj fgd cgbvc 1 NULL NULL yr 2 NULL NULL jg 我需要在上面的表上进行自连接,以仅获取匹配的ID。我正在尝试使用以下查询: Select T1.ID, T1.A, T1.B, T2.C From XYZ T1 INNER J
ID A B C
1 abc ygh NULL
2 fgfd bjh NULL
3 jhkj fgd cgbvc
1 NULL NULL yr
2 NULL NULL jg
我需要在上面的表上进行自连接,以仅获取匹配的ID。我正在尝试使用以下查询:
Select T1.ID, T1.A, T1.B, T2.C
From XYZ T1
INNER JOIN XYZ T2
where T1.ID = T2.ID
但没有得到以下结果:
1 abc ygh yr
2 fgfd bjh jg
请告知。奎师那我猜你想要这样的东西:
select T1.ID, T1.A, T1.B, T2.C from XYZ T1
inner join XYZ T2
on T1.ID = T2.ID
where T1.A is not null and T1.B is not null and T2.C is not null
由于对自身的联接将提供
T1
和T2
的所有组合,因此您需要一个所有列均不为null的联接
为什么要使用自联接
提示:“A'+NULL=NULL
select ID,max(A) A,max(B) B,max(C) C
from XYZ
where A+B+C is null
group by ID
您可以使用下面的查询,但它基于WHERE子句
select ID,max(A) A,max(B) B,max(C) C
from XYZ
where A+B+C is null
group by ID
select ID,A,B,C from (
select *, ROW_NUMBER() over (partition by id order by s desc ) as 'x' from (
Select T1.ID,T1.A,T1.B,T2.C,ROW_NUMBER() over (partition by t1.id order by
t1.a,t1.b ,t1.c ) as s
From xyz T1 JOIN xyz T2 on T1.ID = T2.ID ) abc ) xyz
where x = 1
给定此表结构,您还可以使用
COALESCE
:
SELECT
COALESCE(a.A, b.A) A,
COALESCE(a.B, b.B) B,
COALESCE(a.C, b.C) C
FROM
XYZ a
JOIN
XYZ b ON a.Id = b.Id
WHERE
a.A IS NULL OR a.B IS NULL OR a.C IS NULL
A,B总是空的还是C总是空的?