doc/src/sgml/ref/create_opclass.sgml - hawq - Git at Google

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 $PostgreSQL: pgsql/doc/src/sgml/ref/create_opclass.sgml,v 1.18 2006/10/16 17:28:03 momjian 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</refpurpose>
  </refnamediv>

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

  <refsynopsisdiv>
 <synopsis>
 CREATE OPERATOR CLASS <replaceable class="parameter">name</replaceable> [ DEFAULT ] FOR TYPE <replaceable class="parameter">data_type</replaceable> USING <replaceable class="parameter">index_method</replaceable> AS
   {  OPERATOR <replaceable class="parameter">strategy_number</replaceable> <replaceable class="parameter">operator_name</replaceable> [ ( <replaceable class="parameter">op_type</replaceable>, <replaceable class="parameter">op_type</replaceable> ) ] [ RECHECK ]
    | FUNCTION <replaceable class="parameter">support_number</replaceable> <replaceable class="parameter">funcname</replaceable> ( <replaceable class="parameter">argument_type</replaceable> [, ...] )
    | STORAGE <replaceable class="parameter">storage_type</replaceable>
   } [, ... ]
 </synopsis>
  </refsynopsisdiv>

  <refsect1>
   <title>Description</title>

   <para>
    <command>CREATE OPERATOR CLASS</command> creates a new operator class.
    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
    index method.  The operator class also specifies the support procedures to
    be used by
    the index 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.
    Two operator classes in the same schema can have the same name only if they
    are for different index 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 operator class definition includes all the operators and
    functions required by the index method, nor whether the operators and
    functions form a self-consistent set.  It is the user's
    responsibility to define a valid operator class.
   </para>

   <para>
    Refer to <xref linkend="xindex"> for further information.
   </para>
  </refsect1>

  <refsect1>
   <title>Parameters</title>

   <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
       operator class for its data type.  At most one operator class
       can be the default for a specific data type and index 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">index_method</replaceable></term>
     <listitem>
      <para>
       The name of the index method this operator class is for.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">strategy_number</replaceable></term>
     <listitem>
      <para>
       The index method's strategy number for an operator
       associated with the operator class.
      </para>
     </listitem>
    </varlistentry>

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

    <varlistentry>
     <term><replaceable class="parameter">op_type</replaceable></term>
     <listitem>
      <para>
       The operand data type(s) of an operator, or <literal>NONE</> to
       signify a left-unary or right-unary operator.  The operand 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 rows 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 method's support procedure number for a
       function associated with the operator class.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">funcname</replaceable></term>
     <listitem>
      <para>
       The name (optionally schema-qualified) of a function that is an
       index method support procedure for the operator class.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">argument_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 methods
       (GIN and GiST for now) allow it to be different.  The
       <literal>STORAGE</> clause must be omitted unless the index
       method allows a different type to be used.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   <para>
    The <literal>OPERATOR</>, <literal>FUNCTION</>, and <literal>STORAGE</>
    clauses may appear in any order.
   </para>
  </refsect1>

  <refsect1>
   <title>Notes</title>

   <para>
    Because the index machinery does not check access permissions on functions
    before using them, including a function or operator in an operator class
    is tantamount to granting public execute permission on it.  This is usually
    not an issue for the sorts of functions that are useful in an operator
    class.
   </para>

   <para>
    The operators should not be defined by SQL functions.  A SQL function
    is likely to be inlined into the calling query, which will prevent
    the optimizer from recognizing that the query matches an index.
   </para>
  </refsect1>

  <refsect1>
   <title>Examples</title>

   <para>
    The following example command defines a GiST index operator class
    for the data type <literal>_int4</> (array of <type>int4</type>).  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       @&gt;,
         OPERATOR        8       &lt;@,
         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>
  </refsect1>

  <refsect1>
   <title>Compatibility</title>

   <para>
    <command>CREATE OPERATOR CLASS</command> is a
    <productname>PostgreSQL</productname> extension.  There is no
    <command>CREATE OPERATOR CLASS</command> statement in the SQL
    standard.
   </para>
  </refsect1>

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

   <simplelist type="inline">
    <member><xref linkend="sql-alteropclass" endterm="sql-alteropclass-title"></member>
    <member><xref linkend="sql-dropopclass" endterm="sql-dropopclass-title"></member>
   </simplelist>
  </refsect1>
 </refentry>
	<!--
	$PostgreSQL: pgsql/doc/src/sgml/ref/create_opclass.sgml,v 1.18 2006/10/16 17:28:03 momjian Exp $
	PostgreSQL documentation
	-->

	<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</refpurpose>
	</refnamediv>

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

	<refsynopsisdiv>
	<synopsis>
	CREATE OPERATOR CLASS <replaceable class="parameter">name</replaceable> [ DEFAULT ] FOR TYPE <replaceable class="parameter">data_type</replaceable> USING <replaceable class="parameter">index_method</replaceable> AS
	{ OPERATOR <replaceable class="parameter">strategy_number</replaceable> <replaceable class="parameter">operator_name</replaceable> [ ( <replaceable class="parameter">op_type</replaceable>, <replaceable class="parameter">op_type</replaceable> ) ] [ RECHECK ]
	\| FUNCTION <replaceable class="parameter">support_number</replaceable> <replaceable class="parameter">funcname</replaceable> ( <replaceable class="parameter">argument_type</replaceable> [, ...] )
	\| STORAGE <replaceable class="parameter">storage_type</replaceable>
	} [, ... ]
	</synopsis>
	</refsynopsisdiv>

	<refsect1>
	<title>Description</title>

	<para>
	<command>CREATE OPERATOR CLASS</command> creates a new operator class.
	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
	index method. The operator class also specifies the support procedures to
	be used by
	the index 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.
	Two operator classes in the same schema can have the same name only if they
	are for different index 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 operator class definition includes all the operators and
	functions required by the index method, nor whether the operators and
	functions form a self-consistent set. It is the user's
	responsibility to define a valid operator class.
	</para>

	<para>
	Refer to <xref linkend="xindex"> for further information.
	</para>
	</refsect1>

	<refsect1>
	<title>Parameters</title>

	<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
	operator class for its data type. At most one operator class
	can be the default for a specific data type and index 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">index_method</replaceable></term>
	<listitem>
	<para>
	The name of the index method this operator class is for.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><replaceable class="parameter">strategy_number</replaceable></term>
	<listitem>
	<para>
	The index method's strategy number for an operator
	associated with the operator class.
	</para>
	</listitem>
	</varlistentry>

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

	<varlistentry>
	<term><replaceable class="parameter">op_type</replaceable></term>
	<listitem>
	<para>
	The operand data type(s) of an operator, or <literal>NONE</> to
	signify a left-unary or right-unary operator. The operand 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 rows 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 method's support procedure number for a
	function associated with the operator class.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><replaceable class="parameter">funcname</replaceable></term>
	<listitem>
	<para>
	The name (optionally schema-qualified) of a function that is an
	index method support procedure for the operator class.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><replaceable class="parameter">argument_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 methods
	(GIN and GiST for now) allow it to be different. The
	<literal>STORAGE</> clause must be omitted unless the index
	method allows a different type to be used.
	</para>
	</listitem>
	</varlistentry>
	</variablelist>

	<para>
	The <literal>OPERATOR</>, <literal>FUNCTION</>, and <literal>STORAGE</>
	clauses may appear in any order.
	</para>
	</refsect1>

	<refsect1>
	<title>Notes</title>

	<para>
	Because the index machinery does not check access permissions on functions
	before using them, including a function or operator in an operator class
	is tantamount to granting public execute permission on it. This is usually
	not an issue for the sorts of functions that are useful in an operator
	class.
	</para>

	<para>
	The operators should not be defined by SQL functions. A SQL function
	is likely to be inlined into the calling query, which will prevent
	the optimizer from recognizing that the query matches an index.
	</para>
	</refsect1>

	<refsect1>
	<title>Examples</title>

	<para>
	The following example command defines a GiST index operator class
	for the data type <literal>_int4</> (array of <type>int4</type>). 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>
	</refsect1>

	<refsect1>
	<title>Compatibility</title>

	<para>
	<command>CREATE OPERATOR CLASS</command> is a
	<productname>PostgreSQL</productname> extension. There is no
	<command>CREATE OPERATOR CLASS</command> statement in the SQL
	standard.
	</para>
	</refsect1>

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

	<simplelist type="inline">
	<member><xref linkend="sql-alteropclass" endterm="sql-alteropclass-title"></member>
	<member><xref linkend="sql-dropopclass" endterm="sql-dropopclass-title"></member>
	</simplelist>
	</refsect1>
	</refentry>