检索当前月份和上个月的最后一条记录

Question

I need to get the last recorded value from the current month and the previous month. There are roughly 4,600 records per month.

The following is the code I have tried, however it returns '0' for the two months and not the value:

SELECT a.LogPoint as [Meter]
,max(CASE WHEN c.DateTimeStamp = dateadd(MM,-1,getdate()) THEN c.FloatVALUE ELSE 0 END) as [Total LAST Month]
,max(CASE WHEN c.DateTimeStamp = getdate() THEN c.FloatVALUE ELSE 0 END) as [Total This Month]
FROM 
   SWR.dbo.LoggedEntities a
  ,SWR.dbo.TrendLogRelation b
  ,SWR.dbo.LogTimeValues c
WHERE
      a.GUID = b .GUID
  AND a.Type LIKE 'trend.ETLog'
  AND a.LogPoint = 'WsumOut_Trnd'
  AND b.EntityID = c.ParentID
GROUP BY a.LogPoint

Any help would be greatly appreciated.
Cheers.

Answer 1

I assume the LogPoint is the primary key. correct? In that case check following:

    SELECT mainA.LogPoint AS [Meter],
       lastMonth.FloatValue AS [Total LAST Month],
       thisMonth.FloatValue AS [Total This Month]
FROM SWR.dbo.LoggedEntities mainA
     CROSS APPLY
     (
       SELECT TOP 1 c.FloatVALUE
       FROM SWR.dbo.LoggedEntities a
           JOIN SWR.dbo.TrendLogRelation b ON a.GUID = b.GUID
           JOIN SWR.dbo.LogTimeValues c ON b.EntityID = c.ParentID
       WHERE a.LogPoint = mainA.LogPoint 
       ORDER BY c.DateTimeStamp DESC
     ) thisMonth
    CROSS APPLY
     (
       SELECT TOP 1 c.FloatVALUE
       FROM SWR.dbo.LoggedEntities a
           JOIN SWR.dbo.TrendLogRelation b ON a.GUID = b.GUID
           JOIN SWR.dbo.LogTimeValues c ON b.EntityID = c.ParentID
       WHERE a.LogPoint = mainA.LogPoint AND c.DateTimeStamp <= DATEADD(MM,-1,GETDATE()) 
       ORDER BY c.DateTimeStamp DESC
     ) lastMonth
WHERE a.Type LIKE 'trend.ETLog'
      AND a.LogPoint = 'WsumOut_Trnd';

Just realized that I missed the last month date check. added now. try that :)

Answer 2

getdate() includes both the time and the date, which is why you aren't getting any matches.

One option is to cast both values to dates and then do the comparison.

Answer 3

Two important points before I start:

1. Never use commas in the FROM clause. Always use explicit JOIN syntax.
2. Table aliases should be abbreviations for the table.

Then, you want to use row_number() :

SELECT LogPoint as [Meter],
       max(CASE WHEN seqnum = 1 AND
                     DATEDIFF(month, DateTimeStamp, getdate()) = 1
                THEN cltv.FloatVALUE
           END) as [Total LAST Month],
       max(CASE WHEN seqnum = 1 AND
                     DATEDIFF(month, DateTimeStamp, getdate()) = 0
                THEN ltv.FloatVALUE 
           END) as [Total This Month]
FROM (SELECT le.LogPoint, ltv.DateTimeStamp,
             ROW_NUMBER() OVER (PARTITION BY YEAR(DateTimeStamp), MONTH(DateTimeStamp)
                                ORDER BY DateTimeStamp DESC
                               ) as seqnum
      FROM SWR.dbo.LoggedEntities le JOIN
           SWR.dbo.TrendLogRelation tlr
           ON le.GUID = tlr.GUID JOIN
           SWR.dbo.LogTimeValues ltv
           ON ltr.EntityID = ltv.ParentID
      WHERE le.Type LIKE 'trend.ETLog' AND
            le.LogPoint = 'WsumOut_Trnd' AND
            DATEDIFF(month, ltv.DateTimeStamp, getdate()) IN (0, 1)
     ) x
WHERE seqnum = 1;