Is count(*) really expensive ?

Posted by Anil Namde on Stack Overflow See other posts from Stack Overflow or by Anil Namde
Published on 2010-04-27T10:11:25Z Indexed on 2010/04/27 12:23 UTC
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Filed under:

ASP.NET

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sql-server-2005

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Performance

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performance-tuning

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premature-optimization

I have a page where I have 4 tabs displaying 4 different reports based off different tables.

I obtain the row count of each table using a select count(*) from <table> query and display number of rows available in each table on the tabs. As a result, each page postback causes 5 count(*) queries to be executed (4 to get counts and 1 for pagination) and 1 query for getting the report content.

Now my question is: are count(*) queries really expensive -- should I keep the row counts (at least those that are displayed on the tab) in the view state of page instead of querying multiple times?

How expensive are COUNT(*) queries ?

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