sql - 是否可以加入嵌套查询？

Question

我正在尝试两个嵌套查询。

select * from 
   select a.*, b.* from( 
   (select AAA, BBB from Atable) a) as AA,
   select * from (
   (select QQQ, BBB from Btable)b) as BB
where AA.AAA = 'Y' and AA.BBB = BB.BBB

有可能做这样的事情吗？

Answer 1

你可以做：

select * from 
   (select AAA, BBB from Atable) a
      inner join
   (select QQQ, BBB from Btable)b
      on
         a.BBB = b.BBB
where a.AAA = 'Y'

我不确定您的问题中额外的嵌套和别名级别试图实现什么。

Answer 2

你为什么要改为查询这种类型的查询

select * 
from 
   select a.*, b.* 
   from
       ( 
           (select AAA, BBB from Atable) a) as AA,
           select * 
           from (
                  (select QQQ, BBB from Btable) b) as BB
where 
    AA.AAA = 'Y' and AA.BBB = BB.BBB

您可以像这样使用任何连接，如内连接、左外连接等

select 
    AA.AAA, AA.BBB, BB.QQQ 
from 
    Atable as AA
inner join
    Btable as BB ON BB.BBB = AA.BBB
where
    AA.AAA = 'Y'