Sql 可以加入嵌套查询吗?
我正在尝试两个嵌套查询Sql 可以加入嵌套查询吗?,sql,Sql,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 可以这样做吗?您可以: select * from (select AAA, BBB from At
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
可以这样做吗?您可以:
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的嵌套和别名的额外级别是如何实现的。您为什么要选择这种类型的查询
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
您可以使用任何连接,如内部连接、左侧外部连接等
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'
让我试试这两种选择,如果你愿意,我会回来的needed@TejasVaishnav-如果您使用的数据库引擎有一个像样的优化器(OP没有指出他们在使用什么),那么性能应该是相同的。如果我不知道使用的是什么数据库系统,我肯定会避免使用包含“始终”一词的语句。