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274 lines
8.9 KiB
Plaintext
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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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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEOPCLASS">
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<refmeta>
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<refentrytitle id="sql-createopclass-title">CREATE OPERATOR CLASS</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE OPERATOR CLASS</refname>
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<refpurpose>define a new operator class</refpurpose>
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</refnamediv>
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<indexterm zone="sql-createopclass">
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<primary>CREATE OPERATOR CLASS</primary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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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
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{ 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 ]
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| FUNCTION <replaceable class="parameter">support_number</replaceable> <replaceable class="parameter">funcname</replaceable> ( <replaceable class="parameter">argument_type</replaceable> [, ...] )
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| STORAGE <replaceable class="parameter">storage_type</replaceable>
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} [, ... ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>CREATE OPERATOR CLASS</command> creates a new operator class.
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An operator class defines how a particular data type can be used with
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an index. The operator class specifies that certain operators will fill
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particular roles or <quote>strategies</> for this data type and this
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index method. The operator class also specifies the support procedures to
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be used by
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the index method when the operator class is selected for an
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index column. All the operators and functions used by an operator
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class must be defined before the operator class is created.
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</para>
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<para>
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If a schema name is given then the operator class is created in the
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specified schema. Otherwise it is created in the current schema.
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Two operator classes in the same schema can have the same name only if they
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are for different index methods.
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</para>
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<para>
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The user who defines an operator class becomes its owner. Presently,
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the creating user must be a superuser. (This restriction is made because
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an erroneous operator class definition could confuse or even crash the
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server.)
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</para>
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<para>
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<command>CREATE OPERATOR CLASS</command> does not presently check
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whether the operator class definition includes all the operators and
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functions required by the index method, nor whether the operators and
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functions form a self-consistent set. It is the user's
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responsibility to define a valid operator class.
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</para>
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<para>
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Refer to <xref linkend="xindex"> for further information.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><replaceable class="parameter">name</replaceable></term>
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<listitem>
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<para>
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The name of the operator class to be created. The name may be
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schema-qualified.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>DEFAULT</></term>
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<listitem>
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<para>
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If present, the operator class will become the default
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operator class for its data type. At most one operator class
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can be the default for a specific data type and index method.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">data_type</replaceable></term>
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<listitem>
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<para>
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The column data type that this operator class is for.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">index_method</replaceable></term>
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<listitem>
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<para>
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The name of the index method this operator class is for.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">strategy_number</replaceable></term>
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<listitem>
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<para>
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The index method's strategy number for an operator
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associated with the operator class.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">operator_name</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of an operator associated
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with the operator class.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">op_type</replaceable></term>
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<listitem>
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<para>
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The operand data type(s) of an operator, or <literal>NONE</> to
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signify a left-unary or right-unary operator. The operand data
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types may be omitted in the normal case where they are the same
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as the operator class's data type.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>RECHECK</></term>
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<listitem>
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<para>
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If present, the index is <quote>lossy</> for this operator, and
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so the rows retrieved using the index must be rechecked to
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verify that they actually satisfy the qualification clause
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involving this operator.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">support_number</replaceable></term>
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<listitem>
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<para>
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The index method's support procedure number for a
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function associated with the operator class.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">funcname</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of a function that is an
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index method support procedure for the operator class.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">argument_types</replaceable></term>
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<listitem>
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<para>
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The parameter data type(s) of the function.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">storage_type</replaceable></term>
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<listitem>
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<para>
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The data type actually stored in the index. Normally this is
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the same as the column data type, but some index methods
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(GIN and GiST for now) allow it to be different. The
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<literal>STORAGE</> clause must be omitted unless the index
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method allows a different type to be used.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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The <literal>OPERATOR</>, <literal>FUNCTION</>, and <literal>STORAGE</>
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clauses may appear in any order.
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</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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Because the index machinery does not check access permissions on functions
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before using them, including a function or operator in an operator class
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is tantamount to granting public execute permission on it. This is usually
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not an issue for the sorts of functions that are useful in an operator
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class.
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</para>
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<para>
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The operators should not be defined by SQL functions. A SQL function
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is likely to be inlined into the calling query, which will prevent
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the optimizer from recognizing that the query matches an index.
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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The following example command defines a GiST index operator class
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for the data type <literal>_int4</> (array of <type>int4</type>). See
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<filename>contrib/intarray/</> for the complete example.
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</para>
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<programlisting>
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CREATE OPERATOR CLASS gist__int_ops
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DEFAULT FOR TYPE _int4 USING gist AS
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OPERATOR 3 &&,
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OPERATOR 6 = RECHECK,
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OPERATOR 7 @>,
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OPERATOR 8 <@,
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OPERATOR 20 @@ (_int4, query_int),
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FUNCTION 1 g_int_consistent (internal, _int4, int4),
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FUNCTION 2 g_int_union (bytea, internal),
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FUNCTION 3 g_int_compress (internal),
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FUNCTION 4 g_int_decompress (internal),
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FUNCTION 5 g_int_penalty (internal, internal, internal),
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FUNCTION 6 g_int_picksplit (internal, internal),
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FUNCTION 7 g_int_same (_int4, _int4, internal);
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</programlisting>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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<command>CREATE OPERATOR CLASS</command> is a
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<productname>PostgreSQL</productname> extension. There is no
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<command>CREATE OPERATOR CLASS</command> statement in the SQL
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standard.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alteropclass" endterm="sql-alteropclass-title"></member>
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<member><xref linkend="sql-dropopclass" endterm="sql-dropopclass-title"></member>
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</simplelist>
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</refsect1>
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</refentry>
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