SQL in a Nutshell

Dialects of SQL

The constantly evolving nature of the SQL standard has given rise to a number of SQL dialects among the various vendors and products. These dialects most commonly evolved because the user community of a given database vendor required capabilities in the database before the ANSI committee created a standard. Occasionally though, a new feature is introduced by the academic or research communities due to competitive pressures from competing technologies. For example, many database vendors are augmenting their current programmatic offerings with Java (as is the case with Oracle and Sybase) or VBScript (as Microsoft is doing). In the future, programmers and developers will use these programming languages in concert with SQL to build SQL programs.

Nonetheless, each of these dialects includes conditional processing (such as that controlled through IF . . . THEN statements), control-of-flow functions (such as WHILE loops), variables, and error handling. Because ANSI had not yet developed a standard for these important features, RDBMS developers and vendors were free to create their own commands and syntax. In fact, some of the earliest vendors from the 1980s have variances in the most elementary commands, such as SELECT, because their implementations predate the standards. (ANSI is now refining standards that address these shortcomings.)

Some of these dialects have introduced procedural commands to support the functionality of a much more complete programming language. For ...