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我需要使用带有子查询的 select case 语句将以下过程 if else 语句更改为单个查询...

 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

米属性表结构如下：

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

在该表中 datetime 指的是 emf 更改日期，如果我的输入是“2012-07-17”，则意味着我必须获取该特定日期的新值，在 7 月 15 日至 25 日之间，emf 值为 8.00000。

我使用http://www.dpriver.com/pp/sqlformat.htm格式化了您的代码——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
4

2 回答 2

7

@Michael - 感谢您提供指向http://www.dpriver.com/pp/sqlformat.htm的链接。

试试这个（当然未经测试）

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，如何在http://sqlfiddle.com/上设置一个测试用例

祝你好运！

于 2012-07-25T15:04:36.777 回答
0

没有尝试进行语法检查，我认为您正在寻找这样的东西：

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：一般来说，如果您要获得一个计数来检查零，您可以用EXISTS性能更好的合适的替换它。

于 2012-07-25T15:05:10.550 回答