在日期之间选择第一个值

Question

我有下表：当该日期在 StartDate 和 EndDate 之间时，我需要捕获第一个服务日期，下面是我的语法。

表A

ServiceDate    StartDate    EndDate    ID   PROGRAM
  11/25/15       12/14/15   12/17/15    1    HIGH   
  12/14/15       12/14/15   12/17/15    1    HIGH
  1/20/16        12/14/15   12/14/15    1    HIGH

输出：

       StartDate    EndDate    ID   PROGRAM  FIRST_SERVICE_DT
         12/14/15   12/17/15    1    HIGH      12/14/15

sql

SELECT *, CASE WHEN SERVICEDATE NOT BETWEEN STARTDATE AND ENDDATE THEN NULL
  WHEN SERVICEDATE BETWEEN STARTDATE AND ENDDATE THEN FIRST_VALUE(TRUNC(SERVICEDATE)) OVER (PARTITION BY ID ORDER BY SERVICEDATE)
  ID ORDER BY SERVICEDATE)
  END FIRST_SERVICE_DT

我的查询产生了不正确的结果，需要做什么才能获得我想要的输出？

Answer 1

您可以使用min 窗口函数来做到这一点。

select * 
from (select t.*
      ,min(case when service_date between start_date and end_date then service_date end) over(partition by id) as first_service_date
      from tbl t
     ) t
where service_date=first_service_date