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DocBook XML is superficially compatible with DocBook SGML but has a slightly stricter DTD that we have been violating in a few cases. Although XSLT doesn't care whether the document is valid, the style sheets don't necessarily process invalid documents correctly, so we need to work toward fixing this. This first commit moves the indexterms in refentry elements to an allowed position. It has no impact on the output.
324 lines
11 KiB
Plaintext
324 lines
11 KiB
Plaintext
<!--
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doc/src/sgml/ref/create_opclass.sgml
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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEOPCLASS">
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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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<refmeta>
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<refentrytitle>CREATE OPERATOR CLASS</refentrytitle>
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<manvolnum>7</manvolnum>
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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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<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>
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USING <replaceable class="parameter">index_method</replaceable> [ FAMILY <replaceable class="parameter">family_name</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> ) ] [ FOR SEARCH | FOR ORDER BY <replaceable class="parameter">sort_family_name</replaceable> ]
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| FUNCTION <replaceable class="parameter">support_number</replaceable> [ ( <replaceable class="parameter">op_type</replaceable> [ , <replaceable class="parameter">op_type</replaceable> ] ) ] <replaceable class="parameter">function_name</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 can be 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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Related operator classes can be grouped into <firstterm>operator
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families</>. To add a new operator class to an existing family,
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specify the <literal>FAMILY</> option in <command>CREATE OPERATOR
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CLASS</command>. Without this option, the new class is placed into
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a family named the same as the new class (creating that family if
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it doesn't already exist).
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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 can 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">family_name</replaceable></term>
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<listitem>
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<para>
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The name of the existing operator family to add this operator class to.
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If not specified, a family named the same as the operator class is
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used (creating it, if it doesn't already exist).
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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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In an <literal>OPERATOR</> clause,
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the operand data type(s) of the 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 can 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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<para>
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In a <literal>FUNCTION</> clause, the operand data type(s) the
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function is intended to support, if different from
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the input data type(s) of the function (for B-tree comparison functions
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and hash functions)
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or the class's data type (for B-tree sort support functions and all
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functions in GiST, SP-GiST and GIN operator classes). These defaults
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are correct, and so <replaceable
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class="parameter">op_type</replaceable> need not be specified in
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<literal>FUNCTION</> clauses, except for the case of a B-tree sort
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support function that is meant to support cross-data-type comparisons.
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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">sort_family_name</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of an existing <literal>btree</literal> operator
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family that describes the sort ordering associated with an ordering
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operator.
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</para>
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<para>
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If neither <literal>FOR SEARCH</> nor <literal>FOR ORDER BY</> is
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specified, <literal>FOR SEARCH</> is the default.
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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">function_name</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_type</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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(currently GiST and GIN) 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 can 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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<para>
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Before <productname>PostgreSQL</productname> 8.4, the <literal>OPERATOR</>
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clause could include a <literal>RECHECK</> option. This is no longer
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supported because whether an index operator is <quote>lossy</> is now
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determined on-the-fly at run time. This allows efficient handling of
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cases where an operator might or might not be lossy.
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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 the
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<xref linkend="intarray"> module 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 = (anyarray, anyarray),
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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, int, oid, internal),
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FUNCTION 2 g_int_union (internal, 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"></member>
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<member><xref linkend="sql-dropopclass"></member>
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<member><xref linkend="sql-createopfamily"></member>
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<member><xref linkend="sql-alteropfamily"></member>
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</simplelist>
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</refsect1>
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</refentry>
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