<!--$Header: /cvsroot/pgsql/doc/src/sgml/features.sgml,v 2.20.2.1 2003/11/04 09:45:29 petere Exp $--><appendix id="features"> <title>SQL Conformance</title> <para>  This section attempts to outline to what extent  <productname>PostgreSQL</productname> conforms to the SQL standard.  Full compliance to the standard or a complete statement about the  compliance to the standard is complicated and not particularly  useful, so this section can only give an overview.  </para> <para>  The formal name of the SQL standard is ISO/IEC 9075 <quote>Database  Language SQL</quote>.  A revised version of the standard is released  from time to time; the most recent one appearing in 1999.  That  version is referred to as ISO/IEC 9075:1999, or informally as SQL99.  The version prior to that was SQL92.  <productname>PostgreSQL</productname> development tends to aim for  conformance with the latest official version of the standard where  such conformance does not contradict traditional features or common  sense.  At the time of this writing, balloting is under way for a  new revision of the standard, which, if approved, will eventually  become the conformance target for future  <productname>PostgreSQL</productname> development. </para> <para>  <acronym>SQL92</acronym> defined three feature sets for conformance:  Entry, Intermediate, and Full. Most database management systems claiming  <acronym>SQL</acronym> 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. </para> <para>  <acronym>SQL99</acronym> defines a large set of individual features  rather than the ineffectively broad three levels found in  <acronym>SQL92</acronym>.  A large subset of these features  represents the <quote>core</quote> features, which every conforming  SQL implementation must supply.  The rest of the features are purely  optional.  Some optional features are grouped together to form  <quote>packages</quote>, which SQL implementations can claim  conformance to, thus claiming conformance to particular groups of  features. </para> <para>  The <acronym>SQL99</acronym> standard is also split into 5 parts:  Framework, Foundation, Call Level Interface, Persistent Stored  Modules, and Host Language Bindings.  <productname>PostgreSQL</productname> only covers parts 1, 2, and 5.  Part 3 is similar to the ODBC interface, and part 4 is similar to  the <application>PL/pgSQL</application> programming language, but  exact conformance is not specifically intended in either case. </para> <para>  In the following two sections, we provide a list of those features  that <productname>PostgreSQL</productname> supports, followed by a  list of the features defined in SQL99 which are not yet supported in  <productname>PostgreSQL</productname>.  Both of these lists are  approximate: There may be minor details that are nonconforming for a  feature that is listed as supported, and large parts of an  unsupported feature may in fact be implemented.  The main body of  the documentation always contains the most accurate information  about what does and does not work. </para> <note>  <para>   Feature codes containing a hyphen are subfeatures.  Therefore, if a   particular subfeature is not supported, the main feature is listed   as unsupported even if some other subfeatures are supported.  </para> </note>  <sect1 id="features-sql99">   <title>Supported Features</title>   <para>    <informaltable>     <tgroup cols="4">      <thead>       <row>        <entry>Identifier</entry>        <entry>Package</entry>        <entry>Description</entry>        <entry>Comment</entry>       </row>      </thead>      &features-supported;     </tgroup>    </informaltable>   </para>  </sect1>  <sect1 id="unsupported-features-sql99">   <title>Unsupported Features</title>   <para>    The following features defined in <acronym>SQL99</acronym> are not    implemented in this release of    <productname>PostgreSQL</productname>. In a few cases, equivalent    functionality is available.    <informaltable>     <tgroup cols="4">      <thead>       <row>        <entry>Identifier</entry>        <entry>Package</entry>        <entry>Description</entry>        <entry>Comment</entry>       </row>      </thead>      &features-unsupported;     </tgroup>    </informaltable>   </para>  </sect1> </appendix><!-- Keep this comment at the end of the fileLocal variables:mode:sgmlsgml-omittag:nilsgml-shorttag:tsgml-minimize-attributes:nilsgml-always-quote-attributes:tsgml-indent-step:1sgml-indent-data:tsgml-parent-document:nilsgml-default-dtd-file:"./reference.ced"sgml-exposed-tags:nilsgml-local-catalogs:("/usr/lib/sgml/catalog")sgml-local-ecat-files:nilEnd:-->