Samuel R. Neff wrote:
Dennis,
Do any database systems actually implement this part of the standard? MSSQL
used the term information schema in their MSSQL 2000 version of metadata
access but afaik it was not close to the ANSI standard at all. It's a been
a while for me but I think the Oracle stuff is totally different from what
ANSI spec.
Samuel,
The following is from the PostgreSQL online manual (see
http://www.postgresql.org/docs/8.2/static/features.html ). It is a
pretty good overview of the SQL standards and their implementation. Note
they claim to support 9075-11 which is the information and definition
schema.
SQL-92 defined three feature sets for conformance: Entry, Intermediate,
and Full. Most database management systems claiming SQL standard
conformance were conforming at only the Entry level, since the entire
set of features in the Intermediate and Full levels was either too
voluminous or in conflict with legacy behaviors.
Starting with SQL:1999, the SQL standard defines a large set of
individual features rather than the ineffectively broad three levels
found in SQL-92. A large subset of these features represents the "Core"
features, which every conforming SQL implementation must supply. The
rest of the features are purely optional. Some optional features are
grouped together to form "packages", which SQL implementations can claim
conformance to, thus claiming conformance to particular groups of features.
The SQL:2003 standard is also split into a number of parts. Each is
known by a shorthand name. Note that these parts are not consecutively
numbered.
*
ISO/IEC 9075-1 Framework (SQL/Framework)
*
ISO/IEC 9075-2 Foundation (SQL/Foundation)
*
ISO/IEC 9075-3 Call Level Interface (SQL/CLI)
*
ISO/IEC 9075-4 Persistent Stored Modules (SQL/PSM)
*
ISO/IEC 9075-9 Management of External Data (SQL/MED)
*
ISO/IEC 9075-10 Object Language Bindings (SQL/OLB)
*
ISO/IEC 9075-11 Information and Definition Schemas (SQL/Schemata)
*
ISO/IEC 9075-13 Routines and Types using the Java Language (SQL/JRT)
*
ISO/IEC 9075-14 XML-related specifications (SQL/XML)
PostgreSQL covers parts 1, 2, and 11. Part 3 is similar to the ODBC
interface, and part 4 is similar to the PL/pgSQL programming language,
but exact conformance is not specifically intended or verified in either
case.
PostgreSQL supports most of the major features of SQL:2003. Out of 164
mandatory features required for full Core conformance, PostgreSQL
conforms to at least 150. In addition, there is a long list of supported
optional features. It may be worth noting that at the time of writing,
no current version of any database management system claims full
conformance to Core SQL:2003.
I suspect that IBM's DB2 also supports SQL schema information though I
don't know for sure.
This is another case of where the standard exists and incompatibilities
between different database engines can be removed if they all migrate
towards support of the standard.
Dennis Cote
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