MySQL 引用，以避免重复我自己？

Question

我有这个片段:

SELECT 
    CASE WHEN
        AVG(UNIX_TIMESTAMP(tDone)-UNIX_TIMESTAMP(tIPN))/3600 >= 10
    THEN
        ROUND(AVG(UNIX_TIMESTAMP(tDone)-UNIX_TIMESTAMP(tIPN))/3600,0)
    ELSE
        ROUND(AVG(UNIX_TIMESTAMP(tDone)-UNIX_TIMESTAMP(tIPN))/3600,1)
    END 
FROM
    ...

我可以做些什么来从中删除重复项吗？例如，沿着这些方向的东西:(假设代码如下):

SET var = AVG(UNIX_TIMESTAMP(tDone)-UNIX_TIMESTAMP(tIPN))/3600
SELECT 
    CASE WHEN
        var > 10
    THEN
        ROUND(var,0)
    ELSE
        ROUND(var,1)
    END 
FROM
    ...

Answer 1

使用子查询你可以做这样的事情:

SELECT 
  CASE WHEN avgtiPN >= 10 THEN ROUND(avgtiPN,0) ELSE ROUND(avgtiPN,1) END 
FROM 
  (SELECT 
     AVG(UNIX_TIMESTAMP(tDone)-UNIX_TIMESTAMP(tIPN))/3600 AS avgtiPN
   FROM
    ...) AS AVGQuery

但我仍然不确定它是否更具可读性。