mysql - MySQL 双表 Join 双表

Question

有没有办法从 MySQL 中的虚拟 DUAL 表中加入字段？

说我有一个

SELECT 1 as n1 FROM DUAL

n1
--
 1

和一个

SELECT 2 as n2 FROM DUAL

n2
--
 2

我可以在某种查询中加入两个选择吗？

SELECT 1 as n1 FROM DUAL JOIN (SELECT 2 as n2 FROM DUAL) ON 1=1

?

Answer 1

这是一种方法...

Select t1.n1, t2.n2 
from (select 1 as n1) t1 
CROSS JOIN (Select 2 as n2) t2;

这是另一个

Select t1.n1, t2.n2 
from (select 1 as n1, 'A' as ID) t1 
INNER JOIN (Select 2 as n2, 'A' as ID) t2
  on T1.Id = T2.ID;

你可以做

Select 1 as n1, 2 as n2

但我认为你需要加入是有原因的。