doc/src/sgml/features.sgml

   1 <!-- $PostgreSQL$ -->
   2
   3 <appendix id="features">
   4  <title>SQL Conformance</title>
   5
   6  <para>
   7   This section attempts to outline to what extent
   8   <productname>PostgreSQL</productname> conforms to the current SQL
   9   standard.  The following information is not a full statement of
  10   conformance, but it presents the main topics in as much detail as is
  11   both reasonable and useful for users.
  12  </para>
  13
  14  <para>
  15   The formal name of the SQL standard is ISO/IEC 9075 <quote>Database
  16   Language SQL</quote>.  A revised version of the standard is released
  17   from time to time; the most recent update appearing in 2008.
  18   The 2008 version is referred to as ISO/IEC 9075:2008, or simply as SQL:2008.
  19   The versions prior to that were SQL:2003, SQL:1999, and SQL-92.  Each version
  20   replaces the previous one, so claims of conformance to earlier
  21   versions have no official merit.
  22   <productname>PostgreSQL</productname> development aims for
  23   conformance with the latest official version of the standard where
  24   such conformance does not contradict traditional features or common
  25   sense.  The PostgreSQL project is not represented in the ISO/IEC
  26   9075 Working Group during the preparation of the SQL standard
  27   releases, but even so, many of the features required by the SQL
  28   standard are supported, though sometimes with slightly differing
  29   syntax or function.  Further moves towards conformance can be
  30   expected over time.
  31  </para>
  32
  33  <para>
  34   <acronym>SQL-92</acronym> defined three feature sets for
  35   conformance: Entry, Intermediate, and Full.  Most database
  36   management systems claiming <acronym>SQL</acronym> standard
  37   conformance were conforming at only the Entry level, since the
  38   entire set of features in the Intermediate and Full levels was
  39   either too voluminous or in conflict with legacy behaviors.
  40  </para>
  41
  42  <para>
  43   Starting with <acronym>SQL:1999</acronym>, the SQL standard defines
  44   a large set of individual features rather than the ineffectively
  45   broad three levels found in <acronym>SQL-92</acronym>.  A large
  46   subset of these features represents the <quote>Core</quote>
  47   features, which every conforming SQL implementation must supply.
  48   The rest of the features are purely optional.  Some optional
  49   features are grouped together to form <quote>packages</quote>, which
  50   SQL implementations can claim conformance to, thus claiming
  51   conformance to particular groups of features.
  52  </para>
  53
  54  <para>
  55   The <acronym>SQL:2008</acronym> and <acronym>SQL:2003</acronym>
  56   standard versions are also split into a number
  57   of parts.  Each is known by a shorthand name.  Note that these parts
  58   are not consecutively numbered.
  59
  60   <itemizedlist>
  61    <listitem><para>ISO/IEC 9075-1 Framework (SQL/Framework)</para><indexterm><primary>SQL/Framework</primary></indexterm></listitem>
  62    <listitem><para>ISO/IEC 9075-2 Foundation (SQL/Foundation)</para><indexterm><primary>SQL/Foundation</primary></indexterm></listitem>
  63    <listitem><para>ISO/IEC 9075-3 Call Level Interface (SQL/CLI)</para><indexterm><primary>SQL/CLI</primary></indexterm></listitem>
  64    <listitem><para>ISO/IEC 9075-4 Persistent Stored Modules (SQL/PSM)</para><indexterm><primary>SQL/PSM</primary></indexterm></listitem>
  65    <listitem><para>ISO/IEC 9075-9 Management of External Data (SQL/MED)</para><indexterm><primary>SQL/MED</primary></indexterm></listitem>
  66    <listitem><para>ISO/IEC 9075-10 Object Language Bindings (SQL/OLB)</para><indexterm><primary>SQL/OLB</primary></indexterm></listitem>
  67    <listitem><para>ISO/IEC 9075-11 Information and Definition Schemas (SQL/Schemata)</para><indexterm><primary>SQL/Schemata</primary></indexterm></listitem>
  68    <listitem><para>ISO/IEC 9075-13 Routines and Types using the Java Language (SQL/JRT)</para><indexterm><primary>SQL/JRT</primary></indexterm></listitem>
  69    <listitem><para>ISO/IEC 9075-14 XML-related specifications (SQL/XML)</para><indexterm><primary>SQL/XML</primary></indexterm></listitem>
  70   </itemizedlist>
  71  </para>
  72
  73  <para>
  74   The <productname>PostgreSQL</productname> core covers parts 1, 2, 9,
  75   11, and 14.  Part 3 is covered by the ODBC driver, and part 13 is
  76   covered by the PL/Java plug-in, but exact conformance is currently
  77   not being verified for these components.  There are currently no
  78   implementations of parts 4 and 10
  79   for <productname>PostgreSQL</productname>.
  80  </para>
  81
  82  <para>
  83   PostgreSQL supports most of the major features of SQL:2008.  Out of
  84   179 mandatory features required for full Core conformance,
  85   PostgreSQL conforms to at least 160.  In addition, there is a long
  86   list of supported optional features.  It might be worth noting that at
  87   the time of writing, no current version of any database management
  88   system claims full conformance to Core SQL:2008.
  89  </para>
  90
  91  <para>
  92   In the following two sections, we provide a list of those features
  93   that <productname>PostgreSQL</productname> supports, followed by a
  94   list of the features defined in <acronym>SQL:2008</acronym> which
  95   are not yet supported in <productname>PostgreSQL</productname>.
  96   Both of these lists are approximate: There might be minor details that
  97   are nonconforming for a feature that is listed as supported, and
  98   large parts of an unsupported feature might in fact be implemented.
  99   The main body of the documentation always contains the most accurate
 100   information about what does and does not work.
 101  </para>
 102
 103  <note>
 104   <para>
 105    Feature codes containing a hyphen are subfeatures.  Therefore, if a
 106    particular subfeature is not supported, the main feature is listed
 107    as unsupported even if some other subfeatures are supported.
 108   </para>
 109  </note>
 110
 111   <sect1 id="features-sql-standard">
 112    <title>Supported Features</title>
 113
 114    <para>
 115     <informaltable>
 116      <tgroup cols="4">
 117       <thead>
 118        <row>
 119         <entry>Identifier</entry>
 120         <entry>Package</entry>
 121         <entry>Description</entry>
 122         <entry>Comment</entry>
 123        </row>
 124       </thead>
 125
 126       &features-supported;
 127
 128      </tgroup>
 129     </informaltable>
 130    </para>
 131   </sect1>
 132
 133   <sect1 id="unsupported-features-sql-standard">
 134    <title>Unsupported Features</title>
 135
 136    <para>
 137     The following features defined in <acronym>SQL:2008</acronym> are not
 138     implemented in this release of
 139     <productname>PostgreSQL</productname>. In a few cases, equivalent
 140     functionality is available.
 141
 142     <informaltable>
 143      <tgroup cols="4">
 144       <thead>
 145        <row>
 146         <entry>Identifier</entry>
 147         <entry>Package</entry>
 148         <entry>Description</entry>
 149         <entry>Comment</entry>
 150        </row>
 151       </thead>
 152
 153       &features-unsupported;
 154
 155      </tgroup>
 156     </informaltable>
 157    </para>
 158   </sect1>
 159
 160  </appendix>