SQL Server-將DATEDIFF與子查詢列一起使用

Question

我有一個查詢，看起來像：

SELECT
    col1
    ,...
    ,col3
    ,(SELECT col3 FROM table where <clause>) AS MinPickTime
    ,(SELECT col3 FROM table where <clause>) AS MaxPickTime
    ,DATEDIFF(d, MinPickTime, MaxPickTime)
FROM table

但是，DATEDIFF行不喜歡別名列。

簡而言之，如何給DATEDIFF一個由子查詢派生的別名列？

Answer 1

使用派生表概念來訪問別名。

SELECT  col1
    ,...
    ,col3,
     MinPickTime,
     MaxPickTime ,
DATEDIFF(d, MinPickTime, MaxPickTime)
FROM (
SELECT
    col1
    ,...
    ,col3
    ,(SELECT col3 FROM table where <clause>) AS MinPickTime
    ,(SELECT col3 FROM table where <clause>) AS MaxPickTime

FROM table
)z

Answer 2

with temp as (SELECT
    col1
    ,...
    ,col3
    ,(SELECT col3 FROM table where <clause>) AS MinPickTime
    ,(SELECT col3 FROM table where <clause>) AS MaxPickTime
FROM table)

select DATEDIFF(d,MaxPickTime,MinPickTime) from temp