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$PostgreSQL: pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.48 2007/02/01 00:28:18 momjian Exp $
PostgreSQL documentation
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<refentry id="SQL-CREATEOPERATOR">
 <refmeta>
  <refentrytitle id="sql-createoperator-title">CREATE OPERATOR</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE OPERATOR</refname>
  <refpurpose>define a new operator</refpurpose>
 </refnamediv>

 <indexterm zone="sql-createoperator">
  <primary>CREATE OPERATOR</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
CREATE OPERATOR <replaceable>name</replaceable> (
    PROCEDURE = <replaceable class="parameter">funcname</replaceable>
    [, LEFTARG = <replaceable class="parameter">lefttype</replaceable> ] [, RIGHTARG = <replaceable class="parameter">righttype</replaceable> ]
    [, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ] [, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ]
    [, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ] [, JOIN = <replaceable class="parameter">join_proc</replaceable> ]
    [, HASHES ] [, MERGES ]
)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>CREATE OPERATOR</command> defines a new operator,
   <replaceable class="parameter">name</replaceable>.  The user who
   defines an operator becomes its owner.  If a schema name is given
   then the operator is created in the specified schema.  Otherwise it
   is created in the current schema.
  </para>

  <para>
   The operator name is a sequence of up to <symbol>NAMEDATALEN</>-1
   (63 by default) characters from the following list:
<literallayout>
+ - * / &lt; &gt; = ~ ! @ # % ^ &amp; | ` ?
</literallayout>

   There are a few restrictions on your choice of name:
   <itemizedlist>
    <listitem>
     <para>
     <literal>--</literal> and <literal>/*</literal> cannot appear anywhere in an operator name,
     since they will be taken as the start of a comment.
     </para>
    </listitem>
    <listitem>
     <para>
     A multicharacter operator name cannot end in <literal>+</literal> or
     <literal>-</literal>,
     unless the name also contains at least one of these characters:
<literallayout>
~ ! @ # % ^ &amp; | ` ?
</literallayout>
     For example, <literal>@-</literal> is an allowed operator name,
     but <literal>*-</literal> is not.
     This restriction allows <productname>PostgreSQL</productname> to
     parse SQL-compliant commands without requiring spaces between tokens.
     </para>
    </listitem>
   </itemizedlist>
  </para>

  <para>
   The operator <literal>!=</literal> is mapped to
   <literal>&lt;&gt;</literal> on input, so these two names are always
   equivalent.
  </para>

  <para>
   At least one of <literal>LEFTARG</> and <literal>RIGHTARG</> must be defined.  For
   binary operators, both must be defined. For right  unary
   operators, only <literal>LEFTARG</> should be defined, while for left
   unary operators only <literal>RIGHTARG</> should be defined.
  </para>

  <para>
   The <replaceable class="parameter">funcname</replaceable>
   procedure must have been previously defined using <command>CREATE
   FUNCTION</command> and must be defined to accept the correct number
   of arguments (either one or two) of the indicated types.
  </para>

  <para>
   The other clauses specify optional operator optimization clauses.
   Their meaning is detailed in <xref linkend="xoper-optimization">.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">name</replaceable></term>
      <listitem>
       <para>
        The name of the operator to be defined. See above for allowable
        characters.  The name can be schema-qualified, for example
        <literal>CREATE OPERATOR myschema.+ (...)</>.  If not, then
        the operator is created in the current schema.  Two operators
        in the same schema can have the same name if they operate on
        different data types.  This is called
        <firstterm>overloading</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">funcname</replaceable></term>
      <listitem>
       <para>
        The function used to implement this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">lefttype</replaceable></term>
      <listitem>
       <para>
        The data type of the operator's left operand, if any.
        This option would be omitted for a left-unary operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">righttype</replaceable></term>
      <listitem>
       <para>
        The data type of the operator's right operand, if any.
        This option would be omitted for a right-unary operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">com_op</replaceable></term>
      <listitem>
       <para>
        The commutator of this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">neg_op</replaceable></term>
      <listitem>
       <para>
        The negator of this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">res_proc</replaceable></term>
      <listitem>
       <para>
        The restriction selectivity estimator function for this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">join_proc</replaceable></term>
      <listitem>
       <para>
        The join selectivity estimator function for this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>HASHES</literal></term>
      <listitem>
       <para>
       Indicates this operator can support a hash join.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>MERGES</literal></term>
      <listitem>
       <para>
       Indicates this operator can support a merge join.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>

  <para>
   To give a schema-qualified operator name in <replaceable
   class="parameter">com_op</replaceable> or the other optional
   arguments, use the <literal>OPERATOR()</> syntax, for example:
<programlisting>
COMMUTATOR = OPERATOR(myschema.===) ,
</programlisting>  
  </para>
 </refsect1>
  
 <refsect1>
  <title>Notes</title>

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

  <para>
   The obsolete options <literal>SORT1</>, <literal>SORT2</>,
   <literal>LTCMP</>, and <literal>GTCMP</> were formerly used to
   specify the names of sort operators associated with a mergejoinable
   operator.  This is no longer necessary, since information about
   associated operators is found by looking at btree operator families
   instead.  If one of these options is given, it is ignored except
   for implicitly setting <literal>MERGES</> true.
  </para>

  <para>
   Use <xref linkend="sql-dropoperator"
   endterm="sql-dropoperator-title"> to delete user-defined operators
   from a database.  Use <xref linkend="sql-alteroperator"
   endterm="sql-alteroperator-title"> to modify operators in a
   database.
  </para>
 </refsect1>
  
 <refsect1>
  <title>Examples</title>

  <para>
   The following command defines a new operator, area-equality, for
   the data type <type>box</type>:
<programlisting>
CREATE OPERATOR === (
    LEFTARG = box,
    RIGHTARG = box,
    PROCEDURE = area_equal_procedure,
    COMMUTATOR = ===,
    NEGATOR = !==,
    RESTRICT = area_restriction_procedure,
    JOIN = area_join_procedure,
    HASHES, MERGES
);
</programlisting>  
  </para>
 </refsect1>
 
 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>CREATE OPERATOR</command> is a
   <productname>PostgreSQL</productname> extension.  There are no
   provisions for user-defined operators in the SQL standard.
  </para>
 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="sql-alteroperator" endterm="sql-alteroperator-title"></member>
   <member><xref linkend="sql-createopclass" endterm="sql-createopclass-title"></member>
   <member><xref linkend="sql-dropoperator" endterm="sql-dropoperator-title"></member>
  </simplelist>
 </refsect1>
</refentry>
