基于其他操作结果的MySQL查询操作

Question

我需要根据其他操作结果进行操作。例如：

SELECT 
    SUM(first_column) as res1, 
    SUM(second_column) as res2, 
    res1/res2 as res3 
FROM my_table 

但是，它似乎只能对现有列进行操作。这个用例的解决方法是什么？

Answer 1

您可以使用子查询来实现这一目标。 事情是这样的：

SELECT res1, res2, res1/res2 as res3 
(SELECT SUM(xxx) as res1, SUM(xxx) as res2 
FROM yyy) as subquery 

Answer 2

尝试类似：

SELECT res1/res2 as res3 
FROM (SELECT SUM(xxx) as res1, SUM(xxx) as res2 
     FROM yyy)) 

Answer 3

SELECT res1/res2 as res3 
FROM (SELECT SUM(xxx) as res1, SUM(xxx) as res2 
FROM yyy)) 

这应该工作

Answer 4

您可以使用您的问题这段代码块：

select t.res1 
    ,t.res2 
    ,t.res1/t.res2 as res3 
from (select sum(xxx) as res1 
      ,sum(xxx) as res2 
     from yyy) t 

OR

不推荐，但作品。

select sum(xxx1) as res1 
    ,sum(xxx2) as res2 
    ,sum(xxx1)/sum(xxx2) as res3 
    from yyy 

Answer 5

如果您不需要的中间结果，你可以跳过子查询获得更好的性能：

SELECT SUM(c1)/SUM(c2) AS res FROM t