SQL query to select records which do not exist in a different table with same field structure

I have two tables with two columns in each that have the same structure:



I want to select all of the records in web_site that do NOT have a corresponding match in web_site_prev. I am doing this via an ASP script... currently scrolling through a huge recordset, but that isn't very efficient. How can I do this select in a single statement?

Thank you!
Brad BansnerWeb DeveloperAsked:
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Aneesh RetnakaranDatabase AdministratorCommented:
select * from web_site ws where not exists (select 1 from web_site_prev where  web_site_prev.itemnumber = ws.itemnumber and web_site_prev.category = ws.category )

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Scott PletcherSenior DBACommented:
NOT EXISTS is the best approach.

But you should also create an index on web_site_prev on those two columns; whichever column is more commonly used for lookup and/or more selective should be listed first in the index.
Brad BansnerWeb DeveloperAuthor Commented:
Looks good, thanks so much!
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Microsoft SQL Server

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