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    <p>Really surprising to me... The optimizer takes advantage of parallelism to make the subqueries very efficient. I populated a dummy table with 120K records and tried the below. The third query is only slightly more efficient than the first (yours), but at the cost of more complexity. I would leave yours as-is. There probably is a better solution, but yours looks good enough to me. How long does yours take to process the 80K rows?</p> <pre><code>WITH PCapps2 AS ( SELECT DISTINCT Computer, Sequence, Site, SoftwareName, OS FROM pcapps ) SELECT DISTINCT SoftwareName, Sequence, Site, (SELECT COUNT(p1.SoftwareName) FROM PCapps2 p1 WHERE p1.SoftwareName = pc.Softwarename AND OS = 'Windows 7 Enterprise' AND p1.Site = pc.Site) as 'Win7/site', (SELECT COUNT(p1.SoftwareName) FROM PCapps2 p1 WHERE p1.SoftwareName = pc.Softwarename AND OS = 'Windows 7 Enterprise' AND p1.Sequence = pc.Sequence) as 'Win7Installs/seq', (SELECT COUNT(p2.SoftwareName) FROM PCapps2 p2 WHERE p2.SoftwareName = pc.Softwarename AND OS = 'Windows 7 Enterprise') as TotWin7apps, (SELECT COUNT(p3.SoftwareName) FROM PCapps2 p3 WHERE p3.SoftwareName = pc.SoftwareName) as TotalInstalls FROM PCapps2 pc ;WITH PCapps2 AS ( SELECT DISTINCT Computer, Sequence, Site, SoftwareName, OS FROM pcapps ) SELECT DISTINCT SoftwareName, Sequence, Site, COUNT(case when os = 'Windows 7 Enterprise' then 1 end) over (partition by pc.Softwarename,pc.Site) as 'Win7/site', COUNT(case when os = 'Windows 7 Enterprise' then 1 end) over (partition by pc.Softwarename,pc.Sequence) as 'Win7Installs/seq', COUNT(case when os = 'Windows 7 Enterprise' then 1 end) over (partition by pc.Softwarename) as TotWin7apps, COUNT(*) over (partition by pc.Softwarename) as TotalInstalls FROM PCapps2 pc ;WITH PCapps2 AS ( SELECT DISTINCT Computer, Sequence, Site, SoftwareName, OS FROM pcapps ), a as ( select softwarename, site, COUNT(*) as 'Win7/site' from pcapps2 where os = 'Windows 7 Enterprise' group by softwarename, site ), b as ( select softwarename, sequence, COUNT(*) as 'Win7Installs/seq' from pcapps2 where os = 'Windows 7 Enterprise' group by softwarename, sequence ), c as ( select softwarename, COUNT(case when os = 'Windows 7 Enterprise' then 1 end) as TotWin7apps, COUNT(*) as TotalInstalls from pcapps2 group by softwarename ), d as ( select distinct softwarename, sequence, site from pcapps2 ) select d.*, isnull(a.[Win7/site], 0) as [Win7/site], isnull(b.[Win7Installs/seq],0) as [Win7Installs/seq] , isnull(c.TotWin7apps,0) as TotWin7apps, isnull(c.TotalInstalls, 0) as TotalInstalls from d left join a on d.softwarename = a.softwarename and d.site = a.site left join b on d.softwarename = b.softwarename and d.sequence = b.sequence left join c on d.softwarename = c.softwarename </code></pre> <p>First query: Table 'pcapps'. Scan count 15, logical reads 6630, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.</p> <p>Second query: Table 'pcapps'. Scan count 3, logical reads 1326, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 18, logical reads 1983591, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.</p> <p>Third query: Table 'pcapps'. Scan count 12, logical reads 5304, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.</p>
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    1. POOptimize performance of sub-queries
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    1. USKevin Suchlicki
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    1. COThe initial query from several joined tables selects 80,000 records in 38 seconds. The full query with sub-queries ran yesterday and it took 3.5 hours. Using the tips from @JasonCarter, the query runs in under a minute.
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