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282 lines
8.4 KiB
Plaintext
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$PostgreSQL: pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.48 2007/02/01 00:28:18 momjian Exp $
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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEOPERATOR">
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<refmeta>
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<refentrytitle id="sql-createoperator-title">CREATE OPERATOR</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</refname>
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<refpurpose>define a new operator</refpurpose>
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</refnamediv>
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<indexterm zone="sql-createoperator">
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<primary>CREATE OPERATOR</primary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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CREATE OPERATOR <replaceable>name</replaceable> (
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PROCEDURE = <replaceable class="parameter">funcname</replaceable>
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[, LEFTARG = <replaceable class="parameter">lefttype</replaceable> ] [, RIGHTARG = <replaceable class="parameter">righttype</replaceable> ]
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[, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ] [, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ]
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[, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ] [, JOIN = <replaceable class="parameter">join_proc</replaceable> ]
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[, HASHES ] [, MERGES ]
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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</command> defines a new operator,
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<replaceable class="parameter">name</replaceable>. The user who
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defines an operator becomes its owner. If a schema name is given
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then the operator is created in the specified schema. Otherwise it
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is created in the current schema.
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</para>
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<para>
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The operator name is a sequence of up to <symbol>NAMEDATALEN</>-1
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(63 by default) characters from the following list:
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<literallayout>
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+ - * / < > = ~ ! @ # % ^ & | ` ?
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</literallayout>
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There are a few restrictions on your choice of name:
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<itemizedlist>
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<listitem>
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<para>
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<literal>--</literal> and <literal>/*</literal> cannot appear anywhere in an operator name,
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since they will be taken as the start of a comment.
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</para>
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</listitem>
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<listitem>
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<para>
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A multicharacter operator name cannot end in <literal>+</literal> or
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<literal>-</literal>,
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unless the name also contains at least one of these characters:
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<literallayout>
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~ ! @ # % ^ & | ` ?
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</literallayout>
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For example, <literal>@-</literal> is an allowed operator name,
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but <literal>*-</literal> is not.
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This restriction allows <productname>PostgreSQL</productname> to
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parse SQL-compliant commands without requiring spaces between tokens.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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The operator <literal>!=</literal> is mapped to
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<literal><></literal> on input, so these two names are always
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equivalent.
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</para>
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<para>
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At least one of <literal>LEFTARG</> and <literal>RIGHTARG</> must be defined. For
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binary operators, both must be defined. For right unary
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operators, only <literal>LEFTARG</> should be defined, while for left
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unary operators only <literal>RIGHTARG</> should be defined.
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</para>
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<para>
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The <replaceable class="parameter">funcname</replaceable>
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procedure must have been previously defined using <command>CREATE
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FUNCTION</command> and must be defined to accept the correct number
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of arguments (either one or two) of the indicated types.
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</para>
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<para>
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The other clauses specify optional operator optimization clauses.
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Their meaning is detailed in <xref linkend="xoper-optimization">.
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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 to be defined. See above for allowable
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characters. The name can be schema-qualified, for example
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<literal>CREATE OPERATOR myschema.+ (...)</>. If not, then
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the operator is created in the current schema. Two operators
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in the same schema can have the same name if they operate on
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different data types. This is called
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<firstterm>overloading</>.
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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 function used to implement 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">lefttype</replaceable></term>
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<listitem>
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<para>
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The data type of the operator's left operand, if any.
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This option would be omitted for a left-unary 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">righttype</replaceable></term>
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<listitem>
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<para>
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The data type of the operator's right operand, if any.
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This option would be omitted for a right-unary 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">com_op</replaceable></term>
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<listitem>
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<para>
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The commutator of 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">neg_op</replaceable></term>
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<listitem>
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<para>
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The negator of 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">res_proc</replaceable></term>
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<listitem>
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<para>
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The restriction selectivity estimator function for 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">join_proc</replaceable></term>
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<listitem>
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<para>
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The join selectivity estimator function for 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><literal>HASHES</literal></term>
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<listitem>
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<para>
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Indicates this operator can support a hash join.
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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>MERGES</literal></term>
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<listitem>
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<para>
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Indicates this operator can support a merge join.
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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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To give a schema-qualified operator name in <replaceable
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class="parameter">com_op</replaceable> or the other optional
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arguments, use the <literal>OPERATOR()</> syntax, for example:
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<programlisting>
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COMMUTATOR = OPERATOR(myschema.===) ,
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</programlisting>
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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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Refer to <xref linkend="xoper"> for further information.
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</para>
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<para>
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The obsolete options <literal>SORT1</>, <literal>SORT2</>,
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<literal>LTCMP</>, and <literal>GTCMP</> were formerly used to
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specify the names of sort operators associated with a mergejoinable
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operator. This is no longer necessary, since information about
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associated operators is found by looking at btree operator families
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instead. If one of these options is given, it is ignored except
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for implicitly setting <literal>MERGES</> true.
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</para>
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<para>
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Use <xref linkend="sql-dropoperator"
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endterm="sql-dropoperator-title"> to delete user-defined operators
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from a database. Use <xref linkend="sql-alteroperator"
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endterm="sql-alteroperator-title"> to modify operators in a
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database.
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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 command defines a new operator, area-equality, for
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the data type <type>box</type>:
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<programlisting>
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CREATE OPERATOR === (
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LEFTARG = box,
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RIGHTARG = box,
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PROCEDURE = area_equal_procedure,
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COMMUTATOR = ===,
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NEGATOR = !==,
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RESTRICT = area_restriction_procedure,
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JOIN = area_join_procedure,
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HASHES, MERGES
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);
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</programlisting>
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</para>
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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</command> is a
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<productname>PostgreSQL</productname> extension. There are no
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provisions for user-defined operators in the SQL 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-alteroperator" endterm="sql-alteroperator-title"></member>
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<member><xref linkend="sql-createopclass" endterm="sql-createopclass-title"></member>
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<member><xref linkend="sql-dropoperator" endterm="sql-dropoperator-title"></member>
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</simplelist>
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</refsect1>
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</refentry>
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