Question

使用SQL Server 2000

如何避免重复值？

查询

SELECT DISTINCT 
    Modification.dbo.Reference.Dates AS DailyDate, 
    tmp_Cardevent2.PERSONID, 
    tmp_Cardevent2.empname, 
    tmp_cardevent2.cardno, 
    tmp_Cardevent2.titlecode, 
    tmp_Cardevent2.titlename, 
    tmp_Cardevent2.departname, 
    CASE 
      WHEN tmp_Cardevent2.CardEventDate = Modification.dbo.Reference.Dates 
        THEN tmp_Cardevent2.CardEventDate 
        ELSE '-----' 
    END AS EMPDATE, 
    CASE 
      WHEN tmp_Cardevent2.CardEventDate = Modification.dbo.Reference.Dates 
        THEN tmp_Cardevent2.Intime 
        ELSE '-----' 
    END AS INTIME
WHEN tmp_Cardevent2.CardEventDate = Modification.dbo.Reference.Dates 
            THEN tmp_Cardevent2.outtime 
            ELSE '-----' 
        END AS outtime 
    FROM tmp_Cardevent2 
    CROSS JOIN  Modification.dbo.Reference
    ORDER BY 
       PERSONID, DAILYDATE DESC

输出：

DailyDates, Personid, empname, cardno, titlecode, titlename, departname, empdate, intime, outtime

12/30/2008 A201 A Cherian 3201 018 Chief Air Traffic Service Assistant Air Traffic Services ----- ----- 

12/30/2008 A201 A Cherian 3201 018 Chief Air Traffic Service Assistant Air Traffic Services 20081230 07:51:31 15:54:38

12/30/2008 A201 A Cherian 3201 018 Chief Air Traffic Service Assistant Air Traffic Services 20081230 07:51:31 15:54:38

我的查询中有什么问题，为什么会出现重复值？如何避免重复值。

请帮忙解决我的问题。

Answer 1

这些日期是DateTime还是Date？如果他们包含时间，这将是他们不平等的原因。结果格式化后，时间就会被切断。

尝试仅选择这些值的日期部分。

Answer 2

首先，您的给定结果集：

DailyDates  Personid  empname    cardno  titlecode  titlename                            departname            empdate   intime    outtime
----------  --------  ---------  ------  ---------  -----------------------------------  --------------------  --------  --------  --------
12/30/2008  A201      A Cherian  3201    018        Chief Air Traffic Service Assistant  Air Traffic Services  -----     -----    
12/30/2008  A201      A Cherian  3201    018        Chief Air Traffic Service Assistant  Air Traffic Services  20081230  07:51:31  15:54:38
12/30/2008  A201      A Cherian  3201    018        Chief Air Traffic Service Assistant  Air Traffic Services  20081230  07:51:31  15:54:38

与您的给定查询不匹配，查询中没有“outtime”列：

SELECT DISTINCT 
    Modification.dbo.Reference.Dates AS DailyDate
        ,tmp_Cardevent2.PERSONID
        ,tmp_Cardevent2.empname
        ,tmp_cardevent2.cardno
        ,tmp_Cardevent2.titlecode
        ,tmp_Cardevent2.titlename
        ,tmp_Cardevent2.departname
        ,CASE 
             WHEN tmp_Cardevent2.CardEventDate = Modification.dbo.Reference.Dates THEN tmp_Cardevent2.CardEventDate 
             ELSE '-----'
         END AS EMPDATE
        ,CASE
             WHEN tmp_Cardevent2.CardEventDate = Modification.dbo.Reference.Dates THEN tmp_Cardevent2.Intime
             ELSE '-----' 
         END AS INTIME
    FROM tmp_Cardevent2
        CROSS JOIN Modification.dbo.Reference
    ORDER BY PERSONID, DAILYDATE DESC

不知道表模式以及它们之间的关系，以及列数据类型：

Modification.dbo.Reference.Dates
tmp_Cardevent2.CardEventDate
tmp_Cardevent2.Intime

很难理解重复的真正原因是什么。但是，根据问题中的有限信息，一个日期和/或时间列的格式很可能隐藏了值的实际差异。

Answer 3

您可以尝试将另一个选择不同的包围作为子查询，例如

select distinct * from (SELECT DISTINCT 
    Modification.dbo
    ...) q

其中q是必需的，并将查询命名为伪表。

不确定为什么第一个不同的东西不起作用，也许CASE混淆了它的优化器？

虽然使用Distinct仍然获得重复值？

3 个答案: