ANSI SQL and Vendor Implementations One thing that is difficult about writing a book like this on standard SQL is that although there is an ANSI standard for SQL, each database vendor has its own implementation of SQL. With each implementation come variations from the actual standard, enhancements to the standard, and even missing elements from the standard. The expected question is, "Because there is an ANSI standard for SQL, what is so difficult about teaching standard SQL?" The answer to this question begins with the statement that ANSI SQL is just that: a standard. ANSI SQL is not an actual language. To teach you SQL, we had to come up with examples and exercises that involve using one or more implementations of SQL. Because each vendor has its own implementation with its own specifications for the language of SQL, these variations, if not handled properly in this book, could actually cause confusion concerning the syntax of various SQL commands. Therefore, we have tried to stay as close to the ANSI standard as possible, foremost discussing the ANSI standard and then showing examples from different implementations that are very close, if not the same, as the exact syntax that ANSI prescribes. We have, however, accompanied examples of variations among implementations with notes for reminders and tips on what to watch out for. Just remember this: Each implementation differs slightly from other implementations. The most important thing is that you understand the underlying concepts of SQL and its commands. Although slight variations do exist, SQL is basically the same across the board and is very portable from database to database, regardless of the particular implementation.  |
