I can HIGHLY recommend Microsoft SQL Server 2008 T-SQL Fundamentals by Itzik
Ben-Gan.
Even if you aren't sure tha SQL Server is your database system of choice,
the author calls attention to language elements which are specific to T-SQL
and provides examples of both ANSI SQL and T-SQL. There are exercises at the
end of each chapter which help to master the material. It is clearly
written, concise yet readily understandable for those with no SQL experience.
The author also provides some (but not too much) background on set theory
and the basis upon which SQL and the relational database model was created.
This may sound excessively deep, but as a computer information systems
student myself, I found this background information invaluable to my
understanding of how SQL works and why. There is a 2005 version of this book
also, but why not go with the latest, especially when the author also calls
attention to anything which is 2008 specific and usually gives a 2005
alternative. There are two other books in this "series" which build off this
one and these too are excellent though definitely more advanced. They are
all from Microsoft Press.