What Is T-SQL?

Transact-SQL is one of the dialects of SQL. As you go through this book and learn how to use T-SQL, I will mention where the SQL standard is being followed and where the topics you are learning are in addition to the standard. Some of the most ordinary items are actually additions to the ANSI standard SQL, such as indexes and any program flow-of-control statements that you learn about later.

The SQL-99 standard does not mention indexes at all. This is because the standard SQL language is not focused on performance issues on specific databases. The standard is written generically to ensure that you can manipulate and access the data contained on any relational database. The result is that every different database platform has developed its own version of SQL that is slightly different from the others. This was done so that items such as indexes—which the overall standard does not account for—can be added as functionality for your database. Another example of an individual database "tweaking" the SQL standard for its own use is Oracle's PL/SQL.