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select count(*) or select count(OrderID)


select count(*) or select count(OrderID)

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adonetok
adonetok
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Which one is fast to get count of records?
1)select count(*) from order
2)select count(OrderID) from order (OrderID is primary key)
I tested in 3894000 records table but both them are done in 0 second
Cadavre
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adonetok (8/11/2010)
Which one is fast to get count of records?
1)select count(*) from order
2)select count(OrderID) from order (OrderID is primary key)
I tested in 3894000 records table but both them are done in 0 second


They'd have the same execution plans I'd imagine, so the same performance in this particular case.


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(*) Missing rows with nolock
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GilaMonster
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http://sqlinthewild.co.za/index.php/2009/04/14/on-counts/


Gail Shaw
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GilaMonster
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CELKO (8/11/2010)
The table row count (NOT records! quit thinking this is a mag tape file system) is available at the table level, so three is no need to scan the table.


SQL will scan something to get a row count (from SELECT COUNT(*) or SELECT Count(<not nullable column>Wink). Not the table, unless there are no nonclustered indexes, but it will scan an index to do the row count, the one with the fewest leaf pages.


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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