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POSQL Optimize query to get max value
 

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    <p>I have the following query. The part where I do the </p> <pre><code> select for max(Entered_On)..... </code></pre> <p>takes the longest. If I comment out the where cause, it run fast. </p> <pre><code> Select dlp.ParamID, dp.ParamName from data_LocP dlp inner join data_In di on dlp.LocID = di.LocID inner join data_Parms dp on dp.ParamID = di.ParamID inner join map_Loc ml on ml.LocId = dlp.LocId where di.Entered_On = (select max(Entered_On ) from data_In where LocId = dlp.LocID and ParamId = dlp.ParamID) </code></pre> <p>I was wondering if there is a way to optimize this query as the part where I get the Max(Entered_On) takes the longest time. As a FYI, I need the Entered_On to be the max date for a given LocId and ParamId.</p> <p>Here is a more extended code but does not give the max:</p> <pre><code> select * FROM ( SELECT dlp.ParamID, dp.ParamName, dlp.LocID, ml.LocName , di.Entered_On, (GETUTCDATE() - dlp.FreqDays) DueDate, dlp.FreqDays, a.CompanyId, a.SiteID, 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 left join ( select ml.LocId,ms.CompanyId, ms.SiteId from map_Sites ms join map_WaterSystems mw on ms.SiteID = mw.SiteID join map_Locations ml on ml.SysID = mw.SysID ) a on a.LocId = dlp.LocID where dlp.FreqDays is not null AND dlp.FreqDays &lt;&gt; '' ) as a WHERE a.RowNum = 1 and Entered_On &lt; (GETUTCDATE() - FreqDays) </code></pre>
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