SQL for Web Nerds
by Philip Greenspun
This is a free online SQL book by Philip Greenspun. It covers data modeling, simple queries, complex queries, transactions, triggers, views, style, PL/SQL and Java, trees, handling dates in Oracle, limits in Oracle, tuning, data warehousing, foreign and legacy data and normalization.
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Download or read it online for free here:
by Rahul Batra - dreamincode.net
This is a short e-book teaching the basics of SQL assuming no prior knowledge of it. While the examples and text use Ingres as the database management system, the code should work correctly on any SQL compliant database.
by Zed A. Shaw - LCodeTHW
This book will teach you the 80% of SQL you probably need to use it effectively, and will mix in concepts in data modeling at the same time. The book is written for people with no prior database, programming, or SQL knowledge.
by Richard T. Snodgrass - Morgan Kaufmann
Richard Snodgrass and his colleagues have explored temporal data concepts over the last two decades. They now have a fairly complete solution to the problems. This book summarizes their work and presents it in a very accessible and useful way.
by Markus Winand
SQL performance problems are everywhere, everyday. This book is a free SQL tuning e-book for developers. It avoids unnecessary details about database internals but highlights the one topic that is most often neglected: proper indexing.