Inside Microsoft SQL Server 2008: T-SQL Querying
There is only one author that I would blindly recommend to anyone serious about Transact-SQL and that author is Itzik Ben-Gan.
It doesn’t matter if you are a novice, or consider yourself either advanced or even expert, there is always something new and something to learn from him.
Itzik has an outstanding talent to explain difficult and complex topics in a way that anyone can understand them. Be that how a query is logically processed, or how to write an elegant query to solve a problem effectively. And for me this is definitely one of the criterias that seperates good authors from the rest.
The books’ concept that was introduced with the SQL Server 2005 edition is continued, updated, and extended to meet the new features in SQL Server 2008 such as the new HIERARCHYID data type.
A very welcome addition to the SQL Server 2008 edition is the chapter about set theory and predicate logic, written by fellow MVP, Steve Kass. It makes the book even more worth reading.
An undisputed recommendation.