我有一个表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
我需要做自连接上表只得到匹配的标识。我尝试使用下面的查询:
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
请指教。克里希纳
为什么要使用self join
。
Tip: '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
我想你想这样的事情:
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
随着加入到本身会给你T1
和T2
的所有组合,你想要的所有列不null
。
您可以使用下面的查询,但其基于WHERE子句。
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
鉴于这种表的结构,你也可以使用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