If you are into caching and reuse of existing query execution plans, which no doubt excites you as much as it does me, you probably use OPTION(OPTIMIZE FOR UNKNOWN) in most of your queries. If, however, you are not tickled by SQL performance optimization, shame on you, you might want to have a look at this to help make some of your queries run a bit smoother. You can read more about this at OPTIMIZE FOR UNKNOWN – a little known SQL Server 2008 feature , thanks Peter Scharlock