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Without CASCADE, if an extension has an unfullfilled dependency on another extension, CREATE EXTENSION ERRORs out with "required extension ... is not installed". That is annoying, especially when that dependency is an implementation detail of the extension, rather than something the extension's user can make sense of. In addition to CASCADE this also includes a small set of regression tests around CREATE EXTENSION. Author: Petr Jelinek, editorialized by Michael Paquier, Andres Freund Reviewed-By: Michael Paquier, Andres Freund, Jeff Janes Discussion: 557E0520.3040800@2ndquadrant.com
253 lines
8.6 KiB
Plaintext
253 lines
8.6 KiB
Plaintext
<!--
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doc/src/sgml/ref/create_extension.sgml
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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEEXTENSION">
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<indexterm zone="sql-createextension">
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<primary>CREATE EXTENSION</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>CREATE EXTENSION</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE EXTENSION</refname>
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<refpurpose>install an extension</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name</replaceable>
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[ WITH ] [ SCHEMA <replaceable class="parameter">schema_name</replaceable> ]
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[ VERSION <replaceable class="parameter">version</replaceable> ]
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[ FROM <replaceable class="parameter">old_version</replaceable> ]
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[ CASCADE ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>CREATE EXTENSION</command> loads a new extension into the current
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database. There must not be an extension of the same name already loaded.
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</para>
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<para>
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Loading an extension essentially amounts to running the extension's script
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file. The script will typically create new <acronym>SQL</> objects such as
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functions, data types, operators and index support methods.
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<command>CREATE EXTENSION</command> additionally records the identities
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of all the created objects, so that they can be dropped again if
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<command>DROP EXTENSION</command> is issued.
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</para>
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<para>
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Loading an extension requires the same privileges that would be
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required to create its component objects. For most extensions this
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means superuser or database owner privileges are needed.
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The user who runs <command>CREATE EXTENSION</command> becomes the
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owner of the extension for purposes of later privilege checks, as well
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as the owner of any objects created by the extension's script.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><literal>IF NOT EXISTS</></term>
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<listitem>
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<para>
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Do not throw an error if an extension with the same name already
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exists. A notice is issued in this case. Note that there is no
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guarantee that the existing extension is anything like the one that
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would have been created from the currently-available script file.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">extension_name</replaceable></term>
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<listitem>
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<para>
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The name of the extension to be
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installed. <productname>PostgreSQL</productname> will create the
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extension using details from the file
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<literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">schema_name</replaceable></term>
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<listitem>
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<para>
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The name of the schema in which to install the extension's
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objects, given that the extension allows its contents to be
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relocated. The named schema must already exist.
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If not specified, and the extension's control file does not specify a
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schema either, the current default object creation schema is used.
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</para>
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<para>
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If the extension specifies <literal>schema</> in its control file,
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the schema cannot be overriden with <literal>SCHEMA</> clause.
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The <literal>SCHEMA</> clause in this case works as follows:
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<itemizedlist>
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<listitem>
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<para>
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If <replaceable class="parameter">schema_name</replaceable> matches
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the schema in control file, it will be used normally as there is no
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conflict.
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</para>
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</listitem>
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<listitem>
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<para>
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If the <literal>CASCADE</> clause is given, the
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<replaceable class="parameter">schema_name</replaceable> will only
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be used for the missing required extensions which do not specify
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<literal>schema</> in their control files.
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</para>
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</listitem>
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<listitem>
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<para>
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If <replaceable class="parameter">schema_name</replaceable> is not
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the same as the one in extension's control file and the
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<literal>CASCADE</> clause is not given, error will be thrown.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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Remember that the extension itself is not considered to be within any
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schema: extensions have unqualified names that must be unique
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database-wide. But objects belonging to the extension can be within
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schemas.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">version</replaceable></term>
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<listitem>
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<para>
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The version of the extension to install. This can be written as
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either an identifier or a string literal. The default version is
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whatever is specified in the extension's control file.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">old_version</replaceable></term>
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<listitem>
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<para><literal>FROM</> <replaceable class="parameter">old_version</>
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must be specified when, and only when, you are attempting to install
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an extension that replaces an <quote>old style</> module that is just
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a collection of objects not packaged into an extension. This option
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causes <command>CREATE EXTENSION</> to run an alternative installation
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script that absorbs the existing objects into the extension, instead
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of creating new objects. Be careful that <literal>SCHEMA</> specifies
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the schema containing these pre-existing objects.
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</para>
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<para>
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The value to use for <replaceable
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class="parameter">old_version</replaceable> is determined by the
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extension's author, and might vary if there is more than one version
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of the old-style module that can be upgraded into an extension.
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For the standard additional modules supplied with pre-9.1
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<productname>PostgreSQL</productname>, use <literal>unpackaged</>
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for <replaceable class="parameter">old_version</replaceable> when
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updating a module to extension style.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>CASCADE</></term>
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<listitem>
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<para>
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Try to install extension including the required dependencies
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recursively. The <literal>SCHEMA</> option will be propagated
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to the required extensions. Other options are not recursively
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applied when using this clause.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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Before you can use <command>CREATE EXTENSION</> to load an extension
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into a database, the extension's supporting files must be installed.
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Information about installing the extensions supplied with
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<productname>PostgreSQL</productname> can be found in
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<link linkend="contrib">Additional Supplied Modules</link>.
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</para>
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<para>
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The extensions currently available for loading can be identified from the
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<link linkend="view-pg-available-extensions"><structname>pg_available_extensions</structname></link>
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or
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<link linkend="view-pg-available-extension-versions"><structname>pg_available_extension_versions</structname></link>
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system views.
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</para>
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<para>
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For information about writing new extensions, see
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<xref linkend="extend-extensions">.
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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Install the <link linkend="hstore">hstore</link> extension into the
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current database:
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<programlisting>
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CREATE EXTENSION hstore;
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</programlisting>
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</para>
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<para>
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Update a pre-9.1 installation of <literal>hstore</> into
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extension style:
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<programlisting>
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CREATE EXTENSION hstore SCHEMA public FROM unpackaged;
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</programlisting>
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Be careful to specify the schema in which you installed the existing
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<literal>hstore</> objects.
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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<command>CREATE EXTENSION</command> is a <productname>PostgreSQL</>
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extension.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterextension"></member>
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<member><xref linkend="sql-dropextension"></member>
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</simplelist>
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</refsect1>
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</refentry>
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