http://msmvps.com/blogs/robfarley/archive/2008/10/12/doing-the-maths-to-understand-sql-optimiser-choices.aspxThe second of my tips from my talk ( slides and scripts available) was about doing the maths to understand why the SQL Server optimiser behaves in the way that it does - particularly in relation to choosing whether to scan an index/heap, or whether toenCommunityServer 2008.5 SP2 (Build: 40407.4157)