path: root/doc/src/sgml/ref/create_opclass.sgml

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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_opclass.sgml,v 1.4 2002/10/04 22:19:29 tgl Exp $
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<refentry id="SQL-CREATEOPCLASS">
 <refmeta>
  <refentrytitle id="sql-createopclass-title">CREATE OPERATOR CLASS</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   CREATE OPERATOR CLASS
  </refname>
  <refpurpose>
   define a new operator class for indexes
  </refpurpose>
  </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>2002-07-28</date>
  </refsynopsisdivinfo>
  <synopsis>
CREATE OPERATOR CLASS <replaceable class="parameter">name</replaceable> [ DEFAULT ] FOR TYPE <replaceable class="parameter">data_type</replaceable> USING <replaceable class="parameter">access_method</replaceable> AS
  {  OPERATOR <replaceable class="parameter">strategy_number</replaceable> <replaceable class="parameter">operator_id</replaceable> [ ( <replaceable class="parameter">type</replaceable>, <replaceable class="parameter">type</replaceable> ) ] [ RECHECK ]
   | FUNCTION <replaceable class="parameter">support_number</replaceable> <replaceable class="parameter">func_name</replaceable> ( <replaceable class="parameter">parameter_types</replaceable> )
   | STORAGE <replaceable class="parameter">storage_type</replaceable>
  } [, ... ]
  </synopsis>
  
  <refsect2 id="R2-SQL-CREATEOPCLASS-1">
   <refsect2info>
    <date>2002-07-28</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">name</replaceable></term>
      <listitem>
       <para>
	The name of the operator class to be created.
	The name may be schema-qualified.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>DEFAULT</></term>
      <listitem>
       <para>
        If present, the operator class will become the default index
	operator class for its data type.  At most one operator class
	can be the default for a specific data type and access method.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">data_type</replaceable></term>
      <listitem>
       <para>
        The column data type that this operator class is for.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">access_method</replaceable></term>
      <listitem>
       <para>
	The name of the index access method this operator class is for.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">strategy_number</replaceable></term>
      <listitem>
       <para>
        The index access method's strategy number for an operator associated
	with the operator class.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">operator_id</replaceable></term>
      <listitem>
       <para>
	The identifier (optionally schema-qualified) of an operator associated
	with the operator class.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">type</replaceable></term>
      <listitem>
       <para>
        The input data type(s) of an operator, or <literal>NONE</> to
	signify a left-unary or right-unary operator.  The input data types
	may be omitted in the normal case where they are the same as the
	operator class's data type.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>RECHECK</></term>
      <listitem>
       <para>
        If present, the index is <quote>lossy</> for this operator,
	and so the tuples retrieved using the index must be rechecked
	to verify that they actually satisfy the qualification clause
	involving this operator.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">support_number</replaceable></term>
      <listitem>
       <para>
        The index access method's support procedure number for a function
	associated with the operator class.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">func_name</replaceable></term>
      <listitem>
       <para>
        The name (optionally schema-qualified) of a function that is
	an index access method support procedure for the operator class.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">parameter_types</replaceable></term>
      <listitem>
       <para>
        The parameter data type(s) of the function.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">storage_type</replaceable></term>
      <listitem>
       <para>
        The data type actually stored in the index.  Normally this is the
	same as the column data type, but some index access methods (only
	GIST at this writing) allow it to be different.  The
	<literal>STORAGE</> clause must be omitted unless the index access
	method allows a different type to be used.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-SQL-CREATEOPCLASS-2">
   <refsect2info>
    <date>2002-07-28</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>
    <variablelist>
     <varlistentry>
      <term><computeroutput>
CREATE OPERATOR CLASS
       </computeroutput></term>
      <listitem>
       <para>
	Message returned if the operator class is successfully created.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-SQL-CREATEOPCLASS-1">
  <refsect1info>
   <date>2002-07-28</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   <command>CREATE OPERATOR CLASS</command> defines a new operator class,
   <replaceable class="parameter">name</replaceable>.
  </para>
  <para>
   An operator class defines how a particular data type can be used with
   an index.  The operator class specifies that certain operators will fill
   particular roles or <quote>strategies</> for this data type and this
   access method.  The operator class also specifies the support procedures to
   be used by 
   the index access method when the operator class is selected for an
   index column.  All the operators and functions used by an operator
   class must be defined before the operator class is created.
  </para>

  <para>
   If a schema name is given then the operator class is created in the
   specified schema.  Otherwise it is created in the current schema (the one
   at the front of the search path; see <literal>CURRENT_SCHEMA()</>).
   Two operator classes in the same schema can have the same name only if they
   are for different index access methods.
  </para>
  <para>
   The user who defines an operator class becomes its owner.  Presently,
   the creating user must be a superuser.  (This restriction is made because
   an erroneous operator class definition could confuse or even crash the
   server.)
  </para>

  <para>
   <command>CREATE OPERATOR CLASS</command> does not presently check
   whether the class definition includes all the operators and functions
   required by the index access method.  It is the user's
   responsibility to define a valid operator class.
  </para>

  <para>
    Refer to the chapter on interfacing extensions to indexes in the
    <citetitle>PostgreSQL Programmer's Guide</citetitle>
    for further information.
  </para>
  
  <refsect2 id="R2-SQL-CREATEOPCLASS-3">
   <refsect2info>
    <date>2002-07-28</date>
   </refsect2info>
   <title>
    Notes
   </title>
   <para>
    Refer to
    <xref linkend="sql-dropopclass" endterm="sql-dropopclass-title">
    to delete user-defined operator classes from a database.
   </para>
  </refsect2>
 </refsect1>
  
 <refsect1 id="R1-SQL-CREATEOPCLASS-2">
  <title>
   Usage
  </title>
  <para>
   The following example command defines a GiST index operator class
   for data type <literal>_int4</> (array of int4).  See
   <filename>contrib/intarray/</> for the complete example.
  </para>

  <programlisting>
CREATE OPERATOR CLASS gist__int_ops
    DEFAULT FOR TYPE _int4 USING gist AS
        OPERATOR        3       &&,
        OPERATOR        6       =       RECHECK,
        OPERATOR        7       @,
        OPERATOR        8       ~,
        OPERATOR        20      @@ (_int4, query_int),
        FUNCTION        1       g_int_consistent (internal, _int4, int4),
        FUNCTION        2       g_int_union (bytea, internal),
        FUNCTION        3       g_int_compress (internal),
        FUNCTION        4       g_int_decompress (internal),
        FUNCTION        5       g_int_penalty (internal, internal, internal),
        FUNCTION        6       g_int_picksplit (internal, internal),
        FUNCTION        7       g_int_same (_int4, _int4, internal);
  </programlisting>  

  <para>
   The <literal>OPERATOR</>, <literal>FUNCTION</>, and <literal>STORAGE</>
   clauses may appear in any order.
  </para>
 </refsect1>
 
 <refsect1 id="R1-SQL-CREATEOPCLASS-3">
  <title>
   Compatibility
  </title>
  
  <refsect2 id="R2-SQL-CREATEOPCLASS-4">
   <refsect2info>
    <date>2002-07-28</date>
   </refsect2info>
   <title>
    SQL92
   </title>

   <para>
    <command>CREATE OPERATOR CLASS</command>
    is a <productname>PostgreSQL</productname> extension.
    There is no <command>CREATE OPERATOR CLASS</command>
    statement in <acronym>SQL92</acronym>.
   </para>
  </refsect2>
 </refsect1>
</refentry>

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