Question

在我的表MeterReading中，我有

-Id(Primary)
-ProjectMeterId
-MeterRead
-ReadDate
-ReadCount

我有一个给定ProjectMeterId的多个条目。我想只更新ReadDate最小的行的ReadCount（对于给定的ProjectMeterId），即

  Update MeterReading
  set ReadCount = 1234
  where  (ReadDate is minimun for a given ProjectMeterId)

注意：表中有许多ProjectMeterId，因此必须更新多个值。如何在查询中执行此操作，而不声明任何SP，声明表变量和所有??因此，更新所有条目需要10分钟以上。

这就是现在正在做的事情：

 UPDATE TTable
SET TTable.ReadCount= 222   
From
(
  Select * From MeterReading where Id in 
  (
     Select Id From
     (
        SELECT Min(Id)as Id, MIN(ReadDate) as ReadDate, ProjectMeterId  FROM MeterReading 
        WHERE ProjectMeterId IS NOT NULL AND ProjectId IS NOT NULL Group By ProjectMeterId 
     )  as temp1
 )
 ) TTable, 

(
     Select * From MeterReading where Id in
          (
        Select Id From 
         (
        SELECT MIN(ReadDate) as ReadDate, ProjectMeterId  FROM MeterReading 
        WHERE ProjectMeterId IS NOT NULL AND ProjectId IS NOT NULL Group By ProjectMeterId 

     ) as temp2
   )
) STable

Where STable.ProjectMeterId = TTable.ProjectMeterId

但是subQueries中的Min（id）给了我那个具有ProjectMeterId特定的最小Id而不是ReadDate的行。

我该怎么办？

Answer 1

;WITH CTE
     AS (SELECT *,
                MIN(ReadDate) OVER (PARTITION BY ProjectMeterId) AS Mn
         FROM   MeterReading)
UPDATE CTE
SET    ReadCount = 1234
WHERE  ReadDate = Mn

或者

UPDATE m1
SET    ReadCount = 1234
FROM   MeterReading m1
WHERE  NOT EXISTS(SELECT *
                  FROM   MeterReading m2
                  WHERE  m1.ProjectMeterId = m2.ProjectMeterId
                         AND m2.ReadDate < m1.ReadDate)

根据Col3更新具有不同col1，Min（Col2）和Col3的表

1 个答案: