Question

我希望能够在查询的输出上运行自我内部联接。在最简单的情况下，执行自我INNER JOIN非常简单：

SELECT *
FROM A a1 INNER JOIN
A a2 ON
a1.key = a2.key

问题是我需要在另一个内连接的输出上执行此自内连接。像

这样的东西
SELECT * FROM DATA.A A INNER JOIN DATA.B B ON A.key = B.key output /* output is the dataset I am interested in */ INNER JOIN (FROM DATA.A A INNER JOIN DATA.B B ON A.key = B.key output2) /* same code to get output, so that I can self reference */ ON OUTPUT.key_alt = OUTPUT2.key_alt

有可能这样做吗？我无法将output存储在我的数据库中。

Answer 1

在SQL Server中：

我更喜欢使用common table expression来做这类事情。在我看来，它让事情更具可读性。

with cte as (
  select * 
  from data.A as A 
    inner join data.B as B
      on A.key = B.key
)
select ...
from cte as o
  inner join cte as i
    on o.key = i.key

您可以使用标准子查询来实现此目的。

select o.*
from (
  select * 
  from data.A as A 
    inner join data.B as B
      on A.key = B.key
  ) as o
  inner join (
  select * 
  from data.A as A 
    inner join data.B as B
      on A.key = B.key
  ) as i
    on o.key = i.key

SQL：如何自引用INNER JOIN的输出？

1 个答案: