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count(*) vs count(1) or count(id)


count(*) vs count(1) or count(id)

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ashkan sirous
ashkan sirous
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Dear Experts,
I want to know what is difference between count(*), count(id) and count(1) base on performance issues.
We have some quires with count(*) that sometimes throws timeout and we have many Transactions on these tables in our other queries.
we guess that if we change it to count(id) or count(1) it will be better.
Is this change effective?
Any information will be helpful.

Faithfully Yours,
Ashkan

Thanks and regards,
Ashkan
Perry Whittle
Perry Whittle
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Count(*) includes rows with null values whereas count(id) would not include rows with a null id. Unlikely if the id is a primary key though, so it does depend on the column itself to a certain extent.

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malleswarareddy_m
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http://msdn.microsoft.com/en-us/library/ms175997.aspx

Malleswarareddy
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Steve Jones
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Here's an article on this site discussing the issue: http://www.sqlservercentral.com/articles/Performance+Tuning/adviceoncount/808/

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Steve Jones - SSC Editor (5/1/2013)
Here's an article on this site discussing the issue: http://www.sqlservercentral.com/articles/Performance+Tuning/adviceoncount/808/


This is a great article, it's amazing what you can forget over time.... Smile

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