Congratulations on the new job! Head First SQL may be a good place to start if you're unfamiliar with SQL. I think you'll definitely want to get a book about T-SQL specifically, whether you start with Head First SQL or not.
Some books that might be a good starting point for learning Transact-SQL itself are Microsoft® SQL Server® 2008 T-SQL Fundamentals and Beginning T-SQL with Microsoft SQL Server 2005 and 2008.
You may also want to check out some online documentation. On the Transact-SQL wikipedia page, I found some links that might be useful to you:
- Sybase Transact-SQL User's Guide
- Transact-SQL Reference for SQL Server 2000 (MSDN)
- Transact-SQL Reference for SQL Server 2005 (MSDN)
- Transact-SQL Reference for SQL Server 2008 (MSDN)
I hope this helps. Best of luck with the new job.