I'd personally recommend buying plenty of SQL books as you'll always find that what one book is good at, or contains, isnt always necessarily in the other ones.
If you had to buy just one book go for Wrox's Professional SQL Server 2000 Programming by Robert Vieira which is accesible and informative.
I've only been doing SQL for a little while myself and I've found this book invaluable.
Hope this yelps!