Yes, performance is affected by using UDF's in the queries because UDF has to be run for every row in the query. There was article UDF Performance Costs in the August 2002 issue of SQL Server Magazine. There's online version at http://www.sqlmag.com/Articles/Index.cfm?ArticleID=25630, but you've to be a subscriber to access it.

>Hi,
>
>I am considering using a UDF to return a value, the id of the current accounting period. This id is normally used as a filter for nearly all queries, so I am concerned if there is a possible performance over head on UDFs.
>
>Anyone looked into this?
>
>Thanks
>
>Mace