SQL Server 2005, formerly code-named Yukon, introduces a wealth of new T-SQL features and enhancements, which I briefly highlighted in my November 2003 article, "What's New in Yukon T-SQL," InstantDoc ID 40206. But in my opinion, common table expressions (CTEs) are by far the most important and exciting new SQL Server 2005 T-SQL feature. CTEs come in two forms: non-recursive and recursive. In this article, I delve into the details of CTEs. I first discuss non-recursive CTEs, then recursive CTEs in single-parent (tree) scenarios. After you've read the article, see the sidebar "Practice What You've Learned," page 26, to test your CTE skills.