Question

从这个表T2中，我需要通过ID选择每个组中最早的日期，其中Prog是＆＃39; YY＆＃39;并在DATEDIFF中使用EDate：

+----+-----------+-----------+------+
| ID |   SDate   |   Edate   | Prog |
+----+-----------+-----------+------+
|  1 | 4/12/2016 | 5/18/2016 | XX   |
|  1 | 4/1/2016  | 4/4/2016  | YY   |
|  1 | 5/23/2016 | 5/28/2016 | YY   |
|  2 | 9/21/2016 | 9/26/2016 | XX   |
|  2 | 8/7/2016  | 8/9/2016  | YY   |
|  3 | 8/2/2015  | 8/12/2015 | YY   |
|  3 | 4/12/2015 | 4/18/2015 | YY   |
+----+-----------+-----------+------+

然后将表T1中的汇总级别显示为期望输出：

+----+------+-----+-----------+------+
| ID | Name | Age |   SDate   | Days |
+----+------+-----+-----------+------+
|  1 | A    |  52 | 4/1/2016  |    3 |
|  2 | B    |  11 | 8/7/2016  |    2 |
|  3 | C    |  24 | 4/12/2015 |    6 |
+----+------+-----+-----------+------+

尝试：

SELECT 
    T1.ID,
    T1.Name,
    T1.Age,
    MIN(T2.SDate) AS [SDate],
    --DATEDIFF(day,MIN(T2.SDate),T2.EDate) AS [Days]
FROM T1
INNER JOIN T2
    ON T1.ID=T2.ID
WHERE T2.Prog='YY'
GROUP BY 
    T1.ID,
    T1.Name,
    T1.Age

我为Days注释了DATEDIFF函数，因为我不确定如何制定它。显然，像DATEDIFF(day,SELECT MIN(SDate) FROM T2 WHERE Prog='YY','Another Date')这样的东西不会起作用，因为我会得到一个整体的MIN（SDate），它不会被ID分割，我不能SELECT ID,MIN(SDate) FROM T2 WHERE Prog='YY' GROUP BY ID内部子查询，因为DATEDIFF只接受Date字段。

那么在这种情况下，如何为每个分组ID提取MIN（SDate）并为相应的Edate计算DATEDIFF？

Answer 1

使用min窗口函数获取每个id的最小日期，并使用它来计算日期差异。

SELECT ID,NAME,Age,DATEDIFF(DD,SDate,EDate) 
FROM (
SELECT 
    T1.ID,
    T1.Name,
    T1.Age,
    MIN(CASE WHEN T2.PROG = 'YY' THEN T2.SDate END) OVER(PARTITION BY T2.ID) AS [SDate],
    T2.EDate
FROM T1
INNER JOIN T2 ON T1.ID=T2.ID
) x

Answer 2

使用MIN作为窗口函数：

SELECT  T1.ID,
        T1.Name,
        T1.Age,
        DATEDIFF(day,
                 MIN(T2.SDate) OVER PARTITION BY (T1.ID, T1.Name, T1.Age),
                 T2.EDate) AS [Days]
FROM T1
INNER JOIN T2
    ON T1.ID = T2.ID
WHERE T2.Prog = 'YY'

从DATEDIFF中的分组结果中选择最早的日期

2 个答案: