SQL for Web Nerds

This is a free online sql book by Philip Greenspun, with a focus on using relational databases for building web services.

Topics include:

• data modeling
• simple and complex queries
• transactions
• triggers
• views,
• PL/SQL and Java
• trees
• Oracle-specific functionality
• data warehousing
• dealing with foreign and legacy data

Sams Teach Yourself SQL in 24 Hours

This book is aimed at readers with limited or no experience using SQL. It is a tutorial rather than a complete SQL reference, providing plenty of examples and exercises with which to apply the material covered.

Structured Query Language (SQL): a Practical Introduction

This is a good introductory text for learning SQL. It's concise and contains plenty of clear explanations and easy-to-follow examples.