Optimize SQL Sub-Query for Max Value

Question

I have the following query:

    SELECT dlp.ParamID ParamID, dp.ParamName ParamName, dlp.LocID LocationID,    ml.LocName LocationName , di.Entered_On DateEntered,  dlp.FreqDays Frequency  
    FROM data_LocParams dlp 
    INNER JOIN data_Input di on dlp.LocID = di.LocID
    INNER JOIN data_Parameters dp on dp.ParamID = di.ParamID
    INNER JOIN map_Locations ml on ml.LocId =  dlp.LocId
    WHERE ( (dlp.FreqDays IS NOT NULL)  AND di.Entered_On < (GETUTCDATE() -  dlp.FreqDays))
    AND
    di.Entered_On = (select max(Entered_On ) from data_Input where LocId = dlp.LocID
                     and ParamId = dlp.ParamID)

I need assistance on how to optimize this query. The bottleneck seems to be with the followng:

    di.Entered_On = (select max(Entered_On ) from data_Input where LocId = dlp.LocID
                     and ParamId = dlp.ParamID)

Note that for a given Enter_On, I need to get the Max Entered_On date based on LocId and ParamId.

I tried the following but did not get the intended result:

     SELECT * FROM
     (
        SELECT dlp.ParamID ParamID, dp.ParamName ParamName, dlp.LocID LocationID,  ml.LocName LocationName, di.Entered_On DateEntered,  dlp.FreqDays  Frequency,      
      ROW_NUMBER() OVER (PARTITION BY dlp.LocId, dlp.ParamID 
                      ORDER BY di.Entered_On DESC)
         as RowNum            

       FROM data_LocParams dlp 
       INNER JOIN data_Input di on dlp.LocID = di.LocID
       INNER JOIN data_Parameters dp on dp.ParamID = di.ParamID
       INNER JOIN map_Locations ml on ml.LocId =  dlp.LocId
       WHERE  dlp.FreqDays IS NOT NULL       
       ) as a WHERE a.RowNum = 1 and DateEntered < (GETUTCDATE() -   Frequency)

Answer 1

I think you can replace it with a window function on the di table (done here as a subquery). Note that the where clause is not in the subquery, because that effects the rows used for the max() (this is probably the problem in your second query):

SELECT dlp.ParamID ParamID, dp.ParamName ParamName, dlp.LocID LocationID,    ml.LocName LocationName , di.Entered_On DateEntered,  dlp.FreqDays Frequency  
    FROM data_LocParams dlp 
    INNER JOIN (select di.*,
                       max(Entered_On) over (partition by LocId, ParamId) as maxeo
                from data_Input di
               ) di on dlp.LocID = di.LocID
    INNER JOIN data_Parameters dp on dp.ParamID = di.ParamID
    INNER JOIN map_Locations ml on ml.LocId =  dlp.LocId
    WHERE (dlp.FreqDays IS NOT NULL)  AND di.Entered_On = di.maxeo and
          di.Entered_On < (GETUTCDATE() -  dlp.FreqDays)

Answer 2

Try using like this -

select ParamID,
   ParamName,
   LocationID,
   LocationName,
   DateEntered,
   Frequency
from (SELECT dlp.ParamID ParamID,
         dp.ParamName ParamName,
         dlp.LocID LocationID,
         ml.LocName LocationName,
         di.Entered_On DateEntered,
         dlp.FreqDays Frequency,
         row_number() over(partition by di.LocID order by di.Entered_On desc) as rn
FROM   data_LocParams dlp
INNER JOIN data_Input di ON  dlp.LocID = di.LocID
INNER JOIN data_Parameters dp ON  dp.ParamID = di.ParamID
INNER JOIN map_Locations ml ON  ml.LocId = dlp.LocId
WHERE  ((dlp.FreqDays IS NOT NULL) AND di.Entered_On < (GETUTCDATE() - dlp.FreqDays))
) as T
where rn = 1