159 lines
6.4 KiB
Plaintext
159 lines
6.4 KiB
Plaintext
<!-- doc/src/sgml/features.sgml -->
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<appendix id="features">
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<title>SQL Conformance</title>
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<para>
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This section attempts to outline to what extent
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<productname>PostgreSQL</productname> conforms to the current SQL
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standard. The following information is not a full statement of
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conformance, but it presents the main topics in as much detail as is
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both reasonable and useful for users.
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</para>
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<para>
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The formal name of the SQL standard is ISO/IEC 9075 <quote>Database
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Language SQL</quote>. A revised version of the standard is released
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from time to time; the most recent update appearing in 2011.
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The 2011 version is referred to as ISO/IEC 9075:2011, or simply as SQL:2011.
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The versions prior to that were SQL:2008, SQL:2003, SQL:1999, and SQL-92. Each version
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replaces the previous one, so claims of conformance to earlier
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versions have no official merit.
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<productname>PostgreSQL</productname> development aims for
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conformance with the latest official version of the standard where
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such conformance does not contradict traditional features or common
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sense. Many of the features required by the SQL
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standard are supported, though sometimes with slightly differing
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syntax or function. Further moves towards conformance can be
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expected over time.
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</para>
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<para>
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<acronym>SQL-92</acronym> defined three feature sets for
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conformance: Entry, Intermediate, and Full. Most database
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management systems claiming <acronym>SQL</acronym> standard
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conformance were conforming at only the Entry level, since the
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entire set of features in the Intermediate and Full levels was
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either too voluminous or in conflict with legacy behaviors.
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</para>
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<para>
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Starting with <acronym>SQL:1999</acronym>, the SQL standard defines
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a large set of individual features rather than the ineffectively
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broad three levels found in <acronym>SQL-92</acronym>. A large
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subset of these features represents the <quote>Core</quote>
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features, which every conforming SQL implementation must supply.
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The rest of the features are purely optional. Some optional
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features are grouped together to form <quote>packages</quote>, which
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SQL implementations can claim conformance to, thus claiming
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conformance to particular groups of features.
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</para>
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<para>
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The standard versions beginning with <acronym>SQL:2003</acronym>
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are also split into a number
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of parts. Each is known by a shorthand name. Note that these parts
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are not consecutively numbered.
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<itemizedlist>
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<listitem><para>ISO/IEC 9075-1 Framework (SQL/Framework)</para><indexterm><primary>SQL/Framework</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-2 Foundation (SQL/Foundation)</para><indexterm><primary>SQL/Foundation</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-3 Call Level Interface (SQL/CLI)</para><indexterm><primary>SQL/CLI</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-4 Persistent Stored Modules (SQL/PSM)</para><indexterm><primary>SQL/PSM</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-9 Management of External Data (SQL/MED)</para><indexterm><primary>SQL/MED</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-10 Object Language Bindings (SQL/OLB)</para><indexterm><primary>SQL/OLB</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-11 Information and Definition Schemas (SQL/Schemata)</para><indexterm><primary>SQL/Schemata</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-13 Routines and Types using the Java Language (SQL/JRT)</para><indexterm><primary>SQL/JRT</primary></indexterm></listitem>
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<listitem><para>ISO/IEC 9075-14 XML-related specifications (SQL/XML)</para><indexterm><primary>SQL/XML</primary></indexterm></listitem>
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</itemizedlist>
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</para>
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<para>
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The <productname>PostgreSQL</productname> core covers parts 1, 2, 9,
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11, and 14. Part 3 is covered by the ODBC driver, and part 13 is
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covered by the PL/Java plug-in, but exact conformance is currently
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not being verified for these components. There are currently no
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implementations of parts 4 and 10
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for <productname>PostgreSQL</productname>.
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</para>
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<para>
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PostgreSQL supports most of the major features of SQL:2011. Out of
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179 mandatory features required for full Core conformance,
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PostgreSQL conforms to at least 160. In addition, there is a long
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list of supported optional features. It might be worth noting that at
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the time of writing, no current version of any database management
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system claims full conformance to Core SQL:2011.
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</para>
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<para>
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In the following two sections, we provide a list of those features
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that <productname>PostgreSQL</productname> supports, followed by a
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list of the features defined in <acronym>SQL:2011</acronym> which
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are not yet supported in <productname>PostgreSQL</productname>.
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Both of these lists are approximate: There might be minor details that
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are nonconforming for a feature that is listed as supported, and
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large parts of an unsupported feature might in fact be implemented.
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The main body of the documentation always contains the most accurate
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information about what does and does not work.
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</para>
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<note>
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<para>
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Feature codes containing a hyphen are subfeatures. Therefore, if a
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particular subfeature is not supported, the main feature is listed
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as unsupported even if some other subfeatures are supported.
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</para>
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</note>
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<sect1 id="features-sql-standard">
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<title>Supported Features</title>
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<para>
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<informaltable>
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<tgroup cols="4">
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<thead>
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<row>
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<entry>Identifier</entry>
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<entry>Package</entry>
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<entry>Description</entry>
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<entry>Comment</entry>
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</row>
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</thead>
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&features-supported;
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</tgroup>
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</informaltable>
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</para>
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</sect1>
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<sect1 id="unsupported-features-sql-standard">
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<title>Unsupported Features</title>
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<para>
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The following features defined in <acronym>SQL:2011</acronym> are not
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implemented in this release of
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<productname>PostgreSQL</productname>. In a few cases, equivalent
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functionality is available.
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<informaltable>
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<tgroup cols="4">
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<thead>
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<row>
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<entry>Identifier</entry>
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<entry>Package</entry>
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<entry>Description</entry>
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<entry>Comment</entry>
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</row>
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</thead>
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&features-unsupported;
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</tgroup>
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</informaltable>
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</para>
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</sect1>
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</appendix>
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