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$PostgreSQL: pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.43 2004/09/20 00:04:19 neilc Exp $
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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 ]
    [, SORT1 = <replaceable class="parameter">left_sort_op</replaceable> ] [, SORT2 = <replaceable class="parameter">right_sort_op</replaceable> ]
    [, LTCMP = <replaceable class="parameter">less_than_op</replaceable> ] [, GTCMP = <replaceable class="parameter">greater_than_op</replaceable> ]
)
</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">.
  </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 may 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>

     <varlistentry>
      <term><replaceable class="parameter">left_sort_op</replaceable></term>
      <listitem>
       <para>
        If this operator can support a merge join, the less-than
        operator that sorts the left-hand data type of this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">right_sort_op</replaceable></term>
      <listitem>
       <para>
        If this operator can support a merge join, the less-than
        operator that sorts the right-hand data type of this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">less_than_op</replaceable></term>
      <listitem>
       <para>
        If this operator can support a merge join, the less-than
        operator that compares the input data types of this operator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">greater_than_op</replaceable></term>
      <listitem>
       <para>
        If this operator can support a merge join, the greater-than
        operator that compares the input data types of this operator.
       </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>
   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,
    SORT1 = &lt;&lt;&lt;,
    SORT2 = &lt;&lt;&lt;
    -- Since sort operators were given, MERGES is implied.
    -- LTCMP and GTCMP are assumed to be &lt; and &gt; respectively
);
</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>
</refentry>

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