13 Things you should know about statistics and the query optimizer
This article covers >
5. Foldable Expressions
6. Non-foldable Expressions
7. What Happens When the Query Optimizer Can’t Estimate the Cardinality of a SARG?
8. Contradiction Detections
9. Foreign Keys
10. Check Constraints
11. Non-Updating Updates
13. When is the Auto-Update to Statistics Triggered?
I know I'll be reading it several times! (when I get round to it...)