doc/src/sgml/ref/alter_operator.sgml - master - githubmirror/postgres

doc/src/sgml/ref/alter_operator.sgml
237 строк7 KB
Tom Lane
Extend ALTER OPERATOR to allow setting more optimization attributes.
20 окт 2023, 19:28
20 окт 2023, 19:282b5154b
<!--
doc/src/sgml/ref/alter_operator.sgml
PostgreSQL documentation
-->

<refentry id="sql-alteroperator">
 <indexterm zone="sql-alteroperator">
  <primary>ALTER OPERATOR</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>ALTER OPERATOR</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>ALTER OPERATOR</refname>
  <refpurpose>change the definition of an operator</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</replaceable> | NONE } , <replaceable>right_type</replaceable> )
    OWNER TO { <replaceable>new_owner</replaceable> | CURRENT_ROLE | CURRENT_USER | SESSION_USER }

ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</replaceable> | NONE } , <replaceable>right_type</replaceable> )
    SET SCHEMA <replaceable>new_schema</replaceable>

ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</replaceable> | NONE } , <replaceable>right_type</replaceable> )
    SET ( {  RESTRICT = { <replaceable class="parameter">res_proc</replaceable> | NONE }
           | JOIN = { <replaceable class="parameter">join_proc</replaceable> | NONE }
           | COMMUTATOR = <replaceable class="parameter">com_op</replaceable>
           | NEGATOR = <replaceable class="parameter">neg_op</replaceable>
           | HASHES
           | MERGES
          } [, ... ] )
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER OPERATOR</command> changes the definition of
   an operator.
  </para>

  <para>
   You must own the operator to use <command>ALTER OPERATOR</command>.
   To alter the owner, you must be able to <literal>SET ROLE</literal> to the
   new owning role, and that role must have <literal>CREATE</literal>
   privilege on the operator's schema.
   (These restrictions enforce that altering the owner
   doesn't do anything you couldn't do by dropping and recreating the operator.
   However, a superuser can alter ownership of any operator anyway.)
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="parameter">name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of an existing operator.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">left_type</replaceable></term>
    <listitem>
     <para>
      The data type of the operator's left operand; write
      <literal>NONE</literal> if the operator has no left operand.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">right_type</replaceable></term>
    <listitem>
     <para>
      The data type of the operator's right operand.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">new_owner</replaceable></term>
    <listitem>
     <para>
      The new owner of the operator.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">new_schema</replaceable></term>
    <listitem>
     <para>
      The new schema for the operator.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
     <term><replaceable class="parameter">res_proc</replaceable></term>
     <listitem>
       <para>
         The restriction selectivity estimator function for this operator; write NONE to remove existing selectivity estimator.
       </para>
      </listitem>
   </varlistentry>

   <varlistentry>
     <term><replaceable class="parameter">join_proc</replaceable></term>
     <listitem>
       <para>
         The join selectivity estimator function for this operator; write NONE to remove existing selectivity estimator.
       </para>
     </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">com_op</replaceable></term>
    <listitem>
     <para>
      The commutator of this operator. Can only be changed if the operator
      does not have an existing commutator.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">neg_op</replaceable></term>
    <listitem>
     <para>
      The negator of this operator. Can only be changed if the operator does
      not have an existing negator.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>HASHES</literal></term>
    <listitem>
     <para>
      Indicates this operator can support a hash join. Can only be enabled and
      not disabled.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>MERGES</literal></term>
    <listitem>
     <para>
      Indicates this operator can support a merge join. Can only be enabled
      and not disabled.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   Refer to <xref linkend="xoper"/> and
   <xref linkend="xoper-optimization"/> for further information.
  </para>

  <para>
   Since commutators come in pairs that are commutators of each other,
   <literal>ALTER OPERATOR SET COMMUTATOR</literal> will also set the
   commutator of the <replaceable class="parameter">com_op</replaceable>
   to be the target operator.  Likewise, <literal>ALTER OPERATOR SET
   NEGATOR</literal> will also set the negator of
   the <replaceable class="parameter">neg_op</replaceable> to be the
   target operator.  Therefore, you must own the commutator or negator
   operator as well as the target operator.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   Change the owner of a custom operator <literal>a @@ b</literal> for type <type>text</type>:
<programlisting>
ALTER OPERATOR @@ (text, text) OWNER TO joe;
</programlisting>
  </para>

  <para>
   Change the restriction and join selectivity estimator functions of a
   custom operator <literal>a &amp;&amp; b</literal> for
   type <type>int[]</type>:
<programlisting>
ALTER OPERATOR &amp;&amp; (int[], int[]) SET (RESTRICT = _int_contsel, JOIN = _int_contjoinsel);
</programlisting>
  </para>

  <para>
   Mark the <literal>&amp;&amp;</literal> operator as being its own
   commutator:
<programlisting>
ALTER OPERATOR &amp;&amp; (int[], int[]) SET (COMMUTATOR = &amp;&amp;);
</programlisting>
  </para>

 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   There is no <command>ALTER OPERATOR</command> statement in
   the SQL standard.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createoperator"/></member>
   <member><xref linkend="sql-dropoperator"/></member>
  </simplelist>
 </refsect1>
</refentry>