SQL：计算重叠日期范围内的天数

Question

我想计算每个ID的天数，但天数重叠。

ID  STARTDATE   ENDDATE
1   19/12/2012  29/01/2013
1   30/05/2013  14/07/2013
1   15/02/2013  12/03/2013
1   13/03/2013  18/03/2013
1   19/03/2013  26/03/2013
1   27/01/2013  07/04/2013
1   08/04/2013  09/04/2013
2   08/04/2013  14/07/2013
2   30/05/2013  12/07/2013
3   08/04/2013  10/04/2013
3   23/05/2013  30/06/2013

Answer 1

SELECT SUM(DATEDIFF( d,STARTDATE,ENDDATE)) AS [Days],ID
FROM TABLE
GROUP BY ID

或者从MIN / MAX DATE范围获取天数：

SELECT D.ID, SUM(DATEDIFF( d,D.STARTDATE,D.ENDDATE)) AS [Days]
FROM (
SELECT ID, MIN(STARTDATE) AS [STARTDATE], MAX(ENDDATE) AS [ENDATE]
FROM TABLE
GROUP BY ID , MIN(STARTDATE), MAX(ENDDATE) 
) AS D
ORDER BY D.ID