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Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
129 lines
2.9 KiB
Plaintext
129 lines
2.9 KiB
Plaintext
<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/unlisten.sgml,v 1.29 2007/01/31 23:26:04 momjian Exp $
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PostgreSQL documentation
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-->
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<refentry id="SQL-UNLISTEN">
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<refmeta>
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<refentrytitle id="SQL-UNLISTEN-TITLE">UNLISTEN</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>UNLISTEN</refname>
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<refpurpose>stop listening for a notification</refpurpose>
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</refnamediv>
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<indexterm zone="sql-unlisten">
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<primary>UNLISTEN</primary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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UNLISTEN { <replaceable class="PARAMETER">name</replaceable> | * }
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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>UNLISTEN</command> is used to remove an existing
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registration for <command>NOTIFY</command> events.
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<command>UNLISTEN</command> cancels any existing registration of
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the current <productname>PostgreSQL</productname> session as a
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listener on the notification <replaceable
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class="PARAMETER">name</replaceable>. The special wildcard
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<literal>*</literal> cancels all listener registrations for the
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current session.
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</para>
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<para>
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<xref endterm="sql-notify-title" linkend="sql-notify">
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contains a more extensive
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discussion of the use of <command>LISTEN</command> and
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<command>NOTIFY</command>.
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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><replaceable class="PARAMETER">name</replaceable></term>
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<listitem>
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<para>
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Name of a notification (any identifier).
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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>*</literal></term>
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<listitem>
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<para>
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All current listen registrations for this session are cleared.
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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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You can unlisten something you were not listening for; no warning or error
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will appear.
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</para>
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<para>
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At the end of each session, <command>UNLISTEN *</command> is
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automatically executed.
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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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To make a registration:
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<programlisting>
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LISTEN virtual;
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NOTIFY virtual;
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Asynchronous notification "virtual" received from server process with PID 8448.
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</programlisting>
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</para>
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<para>
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Once <command>UNLISTEN</> has been executed, further <command>NOTIFY</>
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commands will be ignored:
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<programlisting>
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UNLISTEN virtual;
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NOTIFY virtual;
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-- no NOTIFY event is received
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</programlisting>
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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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There is no <command>UNLISTEN</command> command in the SQL standard.
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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-listen" endterm="sql-listen-title"></member>
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<member><xref linkend="sql-notify" endterm="sql-notify-title"></member>
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</simplelist>
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</refsect1>
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</refentry>
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