Question

Sql Server 2008 Datediff在select语句中有条件。

我有以下查询，需要帮助了解为什么我会得到这些结果和我的问题的最佳解决方案。

 SELECT DISTINCT l.program, l.id
     ,(DATEDIFF(DAY, B.FIRST_DT , B.FIRST_second_DT))days_between1
     ,(DATEDIFF(DAY, C.FIRST_DT , C.FIRST_second_DT))days_between2      
FROM  l
LEFT JOIN l B ON L.id = B.id AND L.SERVICE_DATE = B.SERVICE_DATE
              AND B.FIRST_DT IS NOT NULL AND B.FIRST_DT IS NOT NULL
              AND l.IS ='0' AND L.FIRST_V_DT IS NOT NULL
LEFT JOIN l C ON L.id = C.id AND L.SERVICE_DATE = C.SERVICE_DATE
              AND C.FIRST_DT IS NOT NULL
              AND C.FIRST_A_DT IS NOT NULL AND L.IS ='1'
              AND L.FIRST_DT IS NOT NULL
WHERE 1=1

我得到了两行

Program    id    daysbetween1      daysbetween2
blue        1        null              3
blue        1         4               null

如何获得一行，如下所示，为什么我会得到两行？

Program    id    daysbetween1      daysbetween2
blue        1        4                3

Answer 1

您可以尝试这种方式：

SELECT l.program, l.id
     ,MAX((DATEDIFF(DAY, B.FIRST_DT , B.FIRST_second_DT))) days_between1
     ,MAX((DATEDIFF(DAY, C.FIRST_DT , C.FIRST_second_DT))) days_between2      
FROM  l
LEFT JOIN l B ON L.id = B.id AND L.SERVICE_DATE = B.SERVICE_DATE
              AND B.FIRST_DT IS NOT NULL AND B.FIRST_DT IS NOT NULL
              AND l.IS ='0' AND L.FIRST_V_DT IS NOT NULL
LEFT JOIN l C ON L.id = C.id AND L.SERVICE_DATE = C.SERVICE_DATE
              AND C.FIRST_DT IS NOT NULL
              AND C.FIRST_A_DT IS NOT NULL AND L.IS ='1'
              AND L.FIRST_DT IS NOT NULL
GROUP BY l.program, l.id

除非您从过滤器的某种动态连接中获取此SQL，否则不需要where条件。

具有选择性陈述条件的约会

1 个答案: