Retrieve last record from current month and previous month - sql

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:
Never use commas in the FROM clause. Always use explicit JOIN syntax.
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;