Join Query based on Date - tsql

Question

I have a table that has time scaled values and I need to be able to scale the values. I am trying to make this as simple as possible however speed of execution is a big player for me.
Let me give you an example of the tblTSS_DataCollection:
SELECT TOP 5
[DataPointID]
,[DatapointDate]
,dc.[DataPointValue]
FROM [tblTSS_DataCollection] dc
Where DatapointID = 1093
This here would return a very simple table:
DataPointID DatapointDate DataPointValue
1093 2012-07-29 00:00:01.000 0.01869818
1093 2012-07-29 00:01:01.000 0.01882841
1093 2012-07-29 00:02:01.000 0.01895865
1093 2012-07-29 00:03:01.000 0.01908888
1093 2012-07-29 00:04:01.000 0.01921912
Now I have another table called tblTSS_ScaleSettings which looks like this:
SELECT [ID]
,[DatapointID]
,[EffectiveDate]
,[ScaleType]
,[ScaleValue]
FROM [tblTSS_ScaleSettings]
Which will return a result something like this:
ID DatapointID EffectiveDate ScaleType ScaleValue
1 1093 2012-07-29 00:03:01.000 * 10.0000
Now what I need to be able to do is something like this:
SELECT TOP 5
dc.[DataPointID]
,[DatapointDate]
,dc.[DataPointValue] AS [DVOld]
,CASE sc.ScaleType
WHEN '*' THEN dc.[DataPointValue] * sc.ScaleValue
WHEN '/' THEN dc.[DataPointValue] / sc.ScaleValue
WHEN '+' THEN dc.[DataPointValue] + sc.ScaleValue
WHEN '-' THEN dc.[DataPointValue] - sc.ScaleValue
ELSE dc.[DataPointValue]
END
AS [DatapointValue]
FROM [tblTSS_DataCollection] dc
JOIN [tblTSS_ScaleSettings] sc
on sc.DatapointID = dc.DatapointID
Where dc.DatapointID = 1093
Which would return:
DataPointID DatapointDate DVOld DatapointValue
1093 2012-07-29 00:00:01.000 0.01869818 0.1869818
1093 2012-07-29 00:01:01.000 0.01882841 0.1882841
1093 2012-07-29 00:02:01.000 0.01895865 0.1895865
1093 2012-07-29 00:03:01.000 0.01908888 0.1908888
1093 2012-07-29 00:04:01.000 0.01921912 0.1921912
However, what is wrong with this is because the scaling EffectiveDate in the table doesn't start until 00:03:01 scaling should start then not on all the records. Scaling should be that scale until the next effectivedate. Sometimes we will have multiple Scales that happen and it changes at different times throughout the year. So I need the Select Query to plan for that.... This is where it gets tricky.
Which would look like this:
DataPointID DatapointDate DVOld DatapointValue
1093 2012-07-29 00:00:01.000 0.01869818 0.01869818
1093 2012-07-29 00:01:01.000 0.01882841 0.01882841
1093 2012-07-29 00:02:01.000 0.01895865 0.01895865
1093 2012-07-29 00:03:01.000 0.01908888 0.1908888
1093 2012-07-29 00:04:01.000 0.01921912 0.1921912
Can someone please help?

Answer 1

Something like this might work for you:
SELECT TOP 5
dc.DataPointID
,DatapointDate
,dc.DataPointValue AS DVOld
,CASE sc.ScaleType
WHEN '*' THEN dc.DataPointValue * sc.ScaleValue
WHEN '/' THEN dc.DataPointValue / sc.ScaleValue
WHEN '+' THEN dc.DataPointValue + sc.ScaleValue
WHEN '-' THEN dc.DataPointValue - sc.ScaleValue
ELSE dc.DataPointValue
END
AS DatapointValue
FROM tblTSS_DataCollection dc
LEFT JOIN tblTSS_ScaleSettings sc
ON sc.DatapointID = dc.DatapointID
AND sc.EffectiveDate = (
SELECT MAX(EffectiveDate)
FROM tblTSS_ScaleSettings
WHERE DatapointID = dc.DatapointID
AND EffectiveDate <= dc.DatapointDate
)
WHERE dc.DatapointID = 1093

Answer 2

would a from clause like this work?
FROM [tblTSS_DataCollection] dc
JOIN sc on sc.DatapointID = dc.DatapointID inner join
(
select datapointid, max(effectivedate) as max_dt
from
[tblTSS_ScaleSettings]
where
effectiveDate <= getdate()
group by datapointID
) mx on
sc.datapointid = mx.datapointid and
sc.effectivedate = mx.max_dt
what you entered should be equivalent to:
SELECT TOP 10
dc.[DataPointID]
,[DatapointDate]
,dc.[DataPointValue] AS [DVOld]
,EffectiveDate
,ScaleType
,ScaleValue
,CASE ScaleType
WHEN '*' THEN dc.[DataPointValue] * ScaleValue
WHEN '/' THEN dc.[DataPointValue] / ScaleValue
WHEN '+' THEN dc.[DataPointValue] + ScaleValue
WHEN '-' THEN dc.[DataPointValue] - ScaleValue
ELSE dc.[DataPointValue]
END
AS [DatapointValue]
FROM [tblTSS_DataCollection] dc inner join
(select DatapointID, max(EffectiveDate) as max_effective,
from tblTSS_ScaleSettings ts
where ts.EffectiveDate <= dc.DatapointDate
group by DatapointID) mx
on dc.datapointid = mx.datapointid and
EffectiveDate = max_effective
Where dc.DatapointID = 1093