如何在case语句使用子查询与MSSQL 2008

我需要的，如果else语句来更改以下程序到使用与子查询的select case语句一个查询...如何在case语句使用子查询与MSSQL 2008

if((select COUNT(*) from pseb.dbo.meterattributedetails where [email protected])=0) 
    select @emf=EMF from pseb.dbo.METERMASTER where [email protected] 
    else if((select COUNT(*) from pseb.dbo.meterattributedetails where [email protected] and dateadd(day,1,@fromdate)<DateTime)>0) 
    select top 1 @emf=oldvalue from pseb.dbo.meterattributedetails where [email protected] and dateadd(day,1,@fromdate)<datetime order by DateTime 
    else 
    select top 1 @emf=newvalue from pseb.dbo.meterattributedetails where [email protected] and DateTime<@fromdate order by DateTime desc

meterattribute表结构是这样的：

AttributeID AttributeName Oldvalue newvalue DateTime meterid 
1   EMF   2.00000   4.00000  2012-07-05 4756 
1   EMF   4.00000   6.00000  2012-07-10 4756 
1   EMF   6.00000   8.00000  2012-07-15 4756 
1   EMF   8.00000  10.00000  2012-07-25 4756

在该表的日期时间

指电动势改变日期，如果我的输入为“2012-07-17”意味着我要取他NEWVALUE针对特定日期,,,在之间7月15日至25日，电动势值为8.00000。

我格式化使用http://www.dpriver.com/pp/sqlformat.htm你的代码 - 迈克尔

IF((SELECT Count(*) 
    FROM pseb.dbo.meterattributedetails 
    WHERE meterid = @meterid) = 0) 
    SELECT @emf = emf 
    FROM pseb.dbo.metermaster 
    WHERE meterid = @meterid 
ELSE IF((SELECT Count(*) 
    FROM pseb.dbo.meterattributedetails 
    WHERE meterid = @meterid 
      AND Dateadd(day, 1, @fromdate) < datetime) > 0) 
    SELECT TOP 1 @emf = oldvalue 
    FROM pseb.dbo.meterattributedetails 
    WHERE meterid = @meterid 
     AND Dateadd(day, 1, @fromdate) < datetime 
    ORDER BY datetime 
ELSE 
    SELECT TOP 1 @emf = newvalue 
    FROM pseb.dbo.meterattributedetails 
    WHERE meterid = @meterid 
     AND datetime < @fromdate 
    ORDER BY datetime DESC

来源

2012-07-25 Saranya Jothiprakasam

你甚至读过这些？ – 2012-07-25 14:25:39

编辑:)。希望你现在可以阅读它。 – Narendra 2012-07-25 14:30:35

+1 @AaronBertrand ...我不应该鼓励你 – whytheq 2012-07-25 17:45:51

@迈克尔 - 感谢链接http://www.dpriver.com/pp/sqlformat.htm。

试试这个（未经测试，当然）

SELECT @emf = CASE 
      WHEN ((SELECT Count(*) 
        FROM pseb.dbo.meterattributedetails 
        WHERE meterid = @meterid) = 0) THEN 
      (SELECT emf 
      FROM pseb.dbo.metermaster 
      WHERE meterid = @meterid) 
      WHEN ((SELECT Count(*) 
        FROM pseb.dbo.meterattributedetails 
        WHERE meterid = @meterid 
          AND Dateadd(day, 1, @fromdate) < datetime) > 0) 
      THEN ( 
      SELECT 
      TOP 1 oldvalue 
      FROM 
      pseb.dbo.meterattributedetails 
      WHERE 
      meterid = @meterid 
      AND Dateadd(day, 1, @fromdate) < datetime 
      ORDER 
      BY datetime) 
      ELSE (SELECT TOP 1 newvalue 
        FROM pseb.dbo.meterattributedetails 
        WHERE meterid = @meterid 
         AND datetime < @fromdate 
        ORDER BY datetime DESC) 
      END

@Saranya：如果这不起作用，怎么样在http://sqlfiddle.com/

好运建立测试用例！

来源

2012-07-25 15:04:36

@michael谢谢你的联系..... – 2012-07-26 04:52:59

Thanq u Dan ...它的工作:) – 2012-07-26 04:53:46

与语法检查没有尝试，我认为你在寻找这样的事情：

select @emf = case 
    when not exists (select 42 from pseb.dbo.meterattributedetails where meterid = @meterid) 
    then (select emf from pseb.dbo.metermaster where meterid = @meterid) 
    when exists (select 42 from pseb.dbo.meterattributedetails where meterid = @meterid and 
    Dateadd(day, 1, @fromdate) < datetime) 
    then (select top 1 oldvalue from pseb.dbo.meterattributedetails where meterid = @meterid and 
     Dateadd(day, 1, @fromdate) < datetime order by datetime) 
    else (select 1 newvalue from pseb.dbo.meterattributedetails where meterid = @meterid and 
    datetime < @fromdate order by datetime desc) 
    end

编辑：在一般情况下，如果你获得计数要检查你为零可以取代它合适的EXISTS具有更好的性能。

来源

2012-07-25 15:05:10 HABO

如何在case语句使用子查询与MSSQL 2008

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