This book is about Structured Query Language. Known familiarly as SQL, it is the standard language of relational databases and the lingua franca of the database world. It has been around for more than 20 years and shows no signs of aging. This is mostly because of numerous revisions: proprietary inventions frequently introduced by database vendors are either adopted into the standard, or become obsolete as the database community moves on. The latest SQL standard was introduced in 1999, and even though ANSI/ISO SQL standards do exist, many of these standards remain rather theoretical and differ significantly from implementation to implementation. That makes it difficult to find an SQL book "that has it all." One author might be biased toward a particular vendor so that you might get a decent Oracle or MS SQL Server book but not necessarily a good SQL one; a single explanation of all SQL ANSI/ISO standards alone would hardly be useful to anyone on a practical level. We believe that only a combination of these two approaches can produce a good result.
The RDBMS world is divided between people who pronounce SQL as "ess-cue-ell" and those who pronounce it as "sequel." This book holds the former as the correct pronunciation, hence the usage "an SQL keyword" rather than "a SQL keyword."
A comparison of modern database vendors shows that Oracle, IBM DB2, and Microsoft SQL Server have and are likely to continue to have the lion's share of the market. This does not mean that other vendors are irrelevant. Some features they offer can meet or even exceed those of the "big three" (as we call them); they have their devoted customers, and they are going to be around for years to come. But because we cannot possibly cover each and every proprietary SQL extension, we decided to concentrate on the "big three" and explain SQL features with an emphasis on how they vary among Oracle, DB2, and MS SQL Server and how they differ from the SQL99 standard.
Sybase Adaptive Server SQL syntax is similar to the Microsoft SQL Server's syntax in many respects, and most of this book's MS SQL Server examples would also work with the Sybase RDBMS.
This book is for readers of all levels — from beginners to advanced users. Our goal was to provide a comprehensive reference that would help everyone who needs to communicate with relational databases, especially in a heterogeneous environment. Programmers and database administrators can find up-to-date information on the SQL standard and the dialects employed by most popular database products. Database users can gain a deeper understanding of the behind-the-scenes processes and help with their daily tasks regardless of which of the three major RDBMS they are working with. Managers evaluating database products will gain an insight into internals of RDBMS technology. For managers who must plan for the RDBMS needs of their organizations, this book also explains the role SQL is playing in modern businesses and what is in store for SQL in the future.