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mehedi
Starting Member
2 Posts |
 Posted - 2007-02-15 : 05:16:18
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| Hello Everyone,1. SELECT count(*) from Table12. SELECT count(COLUMN1) from Table1Is there any performance difference between the above queries?M A A Mehedi Hasan |
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SwePeso
Patron Saint of Lost Yaks
30421 Posts |
Posted - 2007-02-15 : 05:20:28
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| COUNT(*) calculate all recordsCOUNT(Column1) calculated all records for which column1 is not nullPeter LarssonHelsingborg, Sweden |
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mehedi
Starting Member
2 Posts |
Posted - 2007-02-15 : 05:25:27
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| Dear Peter Larsson,Thanks for the quick response. Anyway I want to know is there any performance difference between these two query?M A A Mehedi Hasan |
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SwePeso
Patron Saint of Lost Yaks
30421 Posts |
Posted - 2007-02-15 : 05:44:42
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| Try it. And if you do not like the result, try again.Add index on the table over Column1 column and try again.Remove the index and try again and compare the results.Now add a clustered index and repeat the last process.Compare the timings again.Which result did you come to?Peter LarssonHelsingborg, Sweden |
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Kristen
Test
22859 Posts |
Posted - 2007-02-15 : 06:34:30
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| "Anyway I want to know is there any performance difference between these two query?"Yes, unless COLUMN1 is the only column in the Clustered Index in which case they are probably the same. Even then it might depend on what was cached in memory at the time though.It might also depend on whether SQL Server was confident that DBCC UPDATEUSAGE was current.And it will definitely depend on whether you have a WHERE clause, JOINs, or additional columns in the SELECT list, or not.Kristen |
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differnce between count(*) and count(COLUMN1)