Gonzaga University: Shawn Bowers' "Query Optimization"
Read slides 3 through 20 (pages 2-10) for an overview of cost-based query optimization techniques. As you read this lecture be sure to understand the importance of utilizing the statistical methods for query optimization.
Click http://web.archive.org/web/20140501025019/http://www.cs.gonzaga.edu/~bowers/courses/cpsc421-f09/lecture-18.pdf link to open resource.