Portability

As a bit of a bonus, because we had access to all these DBMSs, we will also be able to give you some information about portability.

We regard portability as a matter of great importance. In the first place, this book is about client/server applications. We anticipate that you will want to write code that works regardless of DBMS. In fact, we anticipate that you may not even know for which DBMS you are coding!

To avoid depending on any vendor's idiosyncrasies, all SQL examples and descriptions of SQL syntax in this book are written in standard SQLthat is, ANSI/ISO SQL:1999whenever possible. When standard SQL omits a feature but it's common to all DBMSsfor example, the CREATE INDEX statementour examples use syntax that will run on most platforms. Where nonstandard and uncommon syntax exists or had to be tested , we have identified it as such. Look for our "Portability" notes; they indicate where syntax other than standard SQL might be required.

To aid you, we've also added comparison charts that highlight differences between the SQL Standard and the Big Eight. In these tables, you'll sometimes see "N/S" in the ANSI SQL row. This means that the SQL Standard considers the feature to be implementation-defined; that is, there is no Standard-specified requirement. Instead, the decision on how to implement the feature is made by the DBMS vendor.

Optimizing SQL for all dialects is different from tuning for a single package. But the coverage in this book is strictly the universal stuff.