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ca4af308c3
We were doing some amazingly complicated things in order to avoid running the very expensive identify_system_timezone() procedure during GUC initialization. But there is an obvious fix for that, which is to do it once during initdb and have initdb install the system-specific default into postgresql.conf, as it already does for most other GUC variables that need system-environment-dependent defaults. This means that the timezone (and log_timezone) settings no longer have any magic behavior in the server. Per discussion.
323 lines
9.9 KiB
Plaintext
323 lines
9.9 KiB
Plaintext
<!--
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doc/src/sgml/ref/set.sgml
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PostgreSQL documentation
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-->
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<refentry id="SQL-SET">
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<refmeta>
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<refentrytitle>SET</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>SET</refname>
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<refpurpose>change a run-time parameter</refpurpose>
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</refnamediv>
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<indexterm zone="sql-set">
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<primary>SET</primary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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SET [ SESSION | LOCAL ] <replaceable class="PARAMETER">configuration_parameter</replaceable> { TO | = } { <replaceable class="PARAMETER">value</replaceable> | '<replaceable class="PARAMETER">value</replaceable>' | DEFAULT }
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SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="PARAMETER">timezone</replaceable> | LOCAL | DEFAULT }
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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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The <command>SET</command> command changes run-time configuration
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parameters. Many of the run-time parameters listed in
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<xref linkend="runtime-config"> can be changed on-the-fly with
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<command>SET</command>.
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(But some require superuser privileges to change, and others cannot
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be changed after server or session start.)
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<command>SET</command> only affects the value used by the current
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session.
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</para>
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<para>
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If <command>SET</command> (or equivalently <command>SET SESSION</command>)
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is issued within a transaction that is later aborted, the effects of the
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<command>SET</command> command disappear when the transaction is rolled
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back. Once the surrounding transaction is committed, the effects
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will persist until the end of the session, unless overridden by another
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<command>SET</command>.
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</para>
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<para>
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The effects of <command>SET LOCAL</command> last only till the end of
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the current transaction, whether committed or not. A special case is
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<command>SET</command> followed by <command>SET LOCAL</command> within
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a single transaction: the <command>SET LOCAL</command> value will be
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seen until the end of the transaction, but afterwards (if the transaction
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is committed) the <command>SET</command> value will take effect.
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</para>
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<para>
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The effects of <command>SET</command> or <command>SET LOCAL</command> are
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also canceled by rolling back to a savepoint that is earlier than the
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command.
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</para>
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<para>
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If <command>SET LOCAL</command> is used within a function that has a
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<literal>SET</> option for the same variable (see
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<xref linkend="sql-createfunction">),
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the effects of the <command>SET LOCAL</command> command disappear at
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function exit; that is, the value in effect when the function was called is
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restored anyway. This allows <command>SET LOCAL</command> to be used for
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dynamic or repeated changes of a parameter within a function, while still
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having the convenience of using the <literal>SET</> option to save and
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restore the caller's value. However, a regular <command>SET</> command
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overrides any surrounding function's <literal>SET</> option; its effects
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will persist unless rolled back.
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</para>
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<note>
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<para>
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In <productname>PostgreSQL</productname> versions 8.0 through 8.2,
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the effects of a <command>SET LOCAL</command> would be canceled by
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releasing an earlier savepoint, or by successful exit from a
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<application>PL/pgSQL</application> exception block. This behavior
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has been changed because it was deemed unintuitive.
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</para>
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</note>
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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>SESSION</></term>
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<listitem>
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<para>
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Specifies that the command takes effect for the current session.
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(This is the default if neither <literal>SESSION</> nor
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<literal>LOCAL</> appears.)
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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>LOCAL</></term>
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<listitem>
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<para>
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Specifies that the command takes effect for only the current
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transaction. After <command>COMMIT</> or <command>ROLLBACK</>,
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the session-level setting takes effect again. Note that
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<command>SET LOCAL</> will appear to have no effect if it is
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executed outside a <command>BEGIN</> block, since the
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transaction will end immediately.
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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">configuration_parameter</replaceable></term>
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<listitem>
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<para>
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Name of a settable run-time parameter. Available parameters are
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documented in <xref linkend="runtime-config"> and below.
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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">value</replaceable></term>
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<listitem>
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<para>
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New value of parameter. Values can be specified as string
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constants, identifiers, numbers, or comma-separated lists of
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these, as appropriate for the particular parameter.
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<literal>DEFAULT</literal> can be written to specify
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resetting the parameter to its default value (that is, whatever
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value it would have had if no <command>SET</> had been executed
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in the current session).
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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Besides the configuration parameters documented in <xref
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linkend="runtime-config">, there are a few that can only be
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adjusted using the <command>SET</command> command or that have a
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special syntax:
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<variablelist>
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<varlistentry>
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<term><literal>SCHEMA</literal></term>
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<listitem>
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<para><literal>SET SCHEMA '<replaceable>value</>'</> is an alias for
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<literal>SET search_path TO <replaceable>value</></>. Only one
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schema can be specified using this syntax.
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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>NAMES</literal></term>
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<listitem>
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<para><literal>SET NAMES <replaceable>value</></> is an alias for
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<literal>SET client_encoding TO <replaceable>value</></>.
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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>SEED</literal></term>
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<listitem>
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<para>
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Sets the internal seed for the random number generator (the
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function <function>random</function>). Allowed values are
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floating-point numbers between -1 and 1, which are then
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multiplied by 2<superscript>31</>-1.
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</para>
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<para>
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The seed can also be set by invoking the function
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<function>setseed</function>:
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<programlisting>
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SELECT setseed(<replaceable>value</replaceable>);
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</programlisting></para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>TIME ZONE</literal></term>
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<listitem>
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<para><literal>SET TIME ZONE <replaceable>value</></> is an alias
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for <literal>SET timezone TO <replaceable>value</></>. The
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syntax <literal>SET TIME ZONE</literal> allows special syntax
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for the time zone specification. Here are examples of valid
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values:
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<variablelist>
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<varlistentry>
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<term><literal>'PST8PDT'</literal></term>
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<listitem>
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<para>
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The time zone for Berkeley, California.
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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>'Europe/Rome'</literal></term>
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<listitem>
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<para>
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The time zone for Italy.
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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>-7</literal></term>
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<listitem>
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<para>
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The time zone 7 hours west from UTC (equivalent
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to PDT). Positive values are east from UTC.
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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>INTERVAL '-08:00' HOUR TO MINUTE</literal></term>
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<listitem>
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<para>
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The time zone 8 hours west from UTC (equivalent
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to PST).
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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>LOCAL</literal></term>
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<term><literal>DEFAULT</literal></term>
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<listitem>
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<para>
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Set the time zone to your local time zone (that is, the
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server's default value of <varname>timezone</>).
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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See <xref linkend="datatype-timezones"> for more information
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about time zones.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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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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The function <function>set_config</function> provides equivalent
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functionality; see <xref linkend="functions-admin">.
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Also, it is possible to UPDATE the
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<link linkend="view-pg-settings"><structname>pg_settings</structname></link>
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system view to perform the equivalent of <command>SET</>.
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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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Set the schema search path:
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<programlisting>
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SET search_path TO my_schema, public;
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</programlisting>
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</para>
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<para>
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Set the style of date to traditional
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<productname>POSTGRES</productname> with <quote>day before month</>
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input convention:
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<screen>
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SET datestyle TO postgres, dmy;
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</screen>
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</para>
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<para>
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Set the time zone for Berkeley, California:
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<screen>
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SET TIME ZONE 'PST8PDT';
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</screen>
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</para>
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<para>
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Set the time zone for Italy:
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<screen>
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SET TIME ZONE 'Europe/Rome';
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</screen></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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<literal>SET TIME ZONE</literal> extends syntax defined in the SQL
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standard. The standard allows only numeric time zone offsets while
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<productname>PostgreSQL</productname> allows more flexible
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time-zone specifications. All other <literal>SET</literal>
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features are <productname>PostgreSQL</productname> extensions.
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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-RESET"></member>
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<member><xref linkend="SQL-SHOW"></member>
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</simplelist>
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</refsect1>
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</refentry>
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