mysql - 如何在 MySQL 中 SUM() 多个子查询行？

Question

问题很简单:我想做:

SELECT SUM((... 一个返回多行的子查询，具有单个 int 值 ...)) AS total;

我该怎么做？我收到一条错误消息，指出子查询返回多行。我需要将它放在子查询中。

Answer 1

这里有一个适合您的方法:

SELECT SUM(column_alias)
FROM (select ... as column_alias from ...) as table_alias

这里有一个具体的虚拟示例来展示实际的方法:

select sum(int_val) 
from (
  select 1 as int_val 
  union
  select 2 as int_val 
  union 
  select 3 as int_val
) as sub;