1.3 SQL Dialects
The constantly evolving nature of the SQL standard has given rise to a number
of SQL dialects among the various vendors and platforms.
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 DB2, 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. Many of these dialects include conditional processing capabilities
(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 at the time users began to demand them, 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 inconsistencies. Some of these dialects have introduced procedural commands to support
the functionality of a much more complete programming language. For
example, these procedural implementations contain error-handling
commands, control-of-flow language, conditional commands, variable
handling, arrays, and many other extensions. Although these are
technically divergent procedural implementations, they are called
dialects here. The SQL/PSM (Persistent Stored Module) package
provides many features associated with programming stored procedures
and incorporates many of the extensions offered by these dialects. Some popular dialects of SQL include:
PL/SQL
Found in Oracle. PL/SQL stands for Procedural Language/SQL and
contains many similarities to the language Ada.
Transact-SQL
Used by both Microsoft SQL Server and Sybase Adaptive Server. As
Microsoft and Sybase have moved away from the common platform they
shared early in the 1990s, their implementations of Transact-SQL have
also diverged.
PL/pgSQL
The name of the SQL dialect and extensions implemented in PostgreSQL.
The acronym stands for Procedural Language/postgreSQL.
SQLPL
The newest dialect is DB2's SQLPL (SQLProcedural
Language), which is based on the standard SQL control statements.
Most of the other dialects predate the standard, meaning
you'll find a lot of variations from the SQL
standard. But since SQLPL came after the standard, it is in greater
compliance.
If you plan to work extensively with a single database system, you
should learn the intricacies of your preferred SQL dialect or
platform. |