The literature on databases is very large, and so the documentation for your particular RDMS is essential. For this book, I use MySQL, but many others are suitable.
Here are a handful of basic textbooks:
Database Systems: A Practical Approach to Design, Implementation, and Management, Thomas Connolly and Carolyn Begg (Pearson Addison Wesley)
A First Course in Database Systems, Jeffrey Ullman (Prentice Hall)
An Introduction to Database Systems, C.J. Date (Pearson Addison Wesley)
MySQL, Paul DuBois (SAMS)
The MySQL Cookbook, Paul DuBois (O'Reilly & Associates)
MySQL and Perl for the Web, Paul DuBois (SAMS)
Programming the Perl DBI, Alligator Descartes and Tim Bunce (O'Reilly)