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-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.30 2002/08/10 19:01:53 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.39 2003/09/22 00:16:57 petere Exp $
PostgreSQL documentation
-->
<refentrytitle id="sql-createoperator-title">CREATE OPERATOR</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
+
<refnamediv>
- <refname>
- CREATE OPERATOR
- </refname>
- <refpurpose>
- define a new operator
- </refpurpose>
- </refnamediv>
+ <refname>CREATE OPERATOR</refname>
+ <refpurpose>define a new operator</refpurpose>
+ </refnamediv>
+
+ <indexterm zone="sql-createoperator">
+ <primary>CREATE OPERATOR</primary>
+ </indexterm>
+
<refsynopsisdiv>
- <refsynopsisdivinfo>
- <date>2000-03-25</date>
- </refsynopsisdivinfo>
- <synopsis>
-CREATE OPERATOR <replaceable>name</replaceable> ( PROCEDURE = <replaceable class="parameter">func_name</replaceable>
- [, LEFTARG = <replaceable class="parameter">lefttype</replaceable>
- ] [, RIGHTARG = <replaceable class="parameter">righttype</replaceable> ]
- [, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ] [, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ]
- [, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ] [, JOIN = <replaceable class="parameter">join_proc</replaceable> ]
- [, HASHES ] [, MERGES ]
- [, SORT1 = <replaceable class="parameter">left_sort_op</replaceable> ] [, SORT2 = <replaceable class="parameter">right_sort_op</replaceable> ]
- [, LTCMP = <replaceable class="parameter">less_than_op</replaceable> ] [, GTCMP = <replaceable class="parameter">greater_than_op</replaceable> ] )
- </synopsis>
-
- <refsect2 id="R2-SQL-CREATEOPERATOR-1">
- <refsect2info>
- <date>2000-03-25</date>
- </refsect2info>
- <title>
- Inputs
- </title>
- <para>
+<synopsis>
+CREATE OPERATOR <replaceable>name</replaceable> (
+ PROCEDURE = <replaceable class="parameter">funcname</replaceable>
+ [, LEFTARG = <replaceable class="parameter">lefttype</replaceable> ] [, RIGHTARG = <replaceable class="parameter">righttype</replaceable> ]
+ [, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ] [, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ]
+ [, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ] [, JOIN = <replaceable class="parameter">join_proc</replaceable> ]
+ [, HASHES ] [, MERGES ]
+ [, SORT1 = <replaceable class="parameter">left_sort_op</replaceable> ] [, SORT2 = <replaceable class="parameter">right_sort_op</replaceable> ]
+ [, LTCMP = <replaceable class="parameter">less_than_op</replaceable> ] [, GTCMP = <replaceable class="parameter">greater_than_op</replaceable> ]
+)
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>
+ <command>CREATE OPERATOR</command> defines a new operator,
+ <replaceable class="parameter">name</replaceable>. The user who
+ defines an operator becomes its owner. If a schema name is given
+ then the operator is created in the specified schema. Otherwise it
+ is created in the current schema.
+ </para>
+
+ <para>
+ The operator name is a sequence of up to <symbol>NAMEDATALEN</>-1
+ (63 by default) characters from the following list:
+<literallayout>
++ - * / < > = ~ ! @ # % ^ & | ` ?
+</literallayout>
+
+ There are a few restrictions on your choice of name:
+ <itemizedlist>
+ <listitem>
+ <para>
+ <literal>--</literal> and <literal>/*</literal> cannot appear anywhere in an operator name,
+ since they will be taken as the start of a comment.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ A multicharacter operator name cannot end in <literal>+</literal> or
+ <literal>-</literal>,
+ unless the name also contains at least one of these characters:
+<literallayout>
+~ ! @ # % ^ & | ` ?
+</literallayout>
+ For example, <literal>@-</literal> is an allowed operator name,
+ but <literal>*-</literal> is not.
+ This restriction allows <productname>PostgreSQL</productname> to
+ parse SQL-compliant commands without requiring spaces between tokens.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ The operator <literal>!=</literal> is mapped to
+ <literal><></literal> on input, so these two names are always
+ equivalent.
+ </para>
+
+ <para>
+ At least one of <literal>LEFTARG</> and <literal>RIGHTARG</> must be defined. For
+ binary operators, both must be defined. For right unary
+ operators, only <literal>LEFTARG</> should be defined, while for left
+ unary operators only <literal>RIGHTARG</> should be defined.
+ </para>
+
+ <para>
+ The <replaceable class="parameter">funcname</replaceable>
+ procedure must have been previously defined using <command>CREATE
+ FUNCTION</command> and must be defined to accept the correct number
+ of arguments (either one or two) of the indicated types.
+ </para>
+
+ <para>
+ The other clauses specify optional operator optimization clauses.
+ Their meaning is detailed in <xref linkend="xoper">.
+ </para>
+ </refsect1>
+
+ <refsect1>
+ <title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
- The operator to be defined. See below for allowable characters.
- The name may be schema-qualified, for example
- <literal>CREATE OPERATOR myschema.+ (...)</>.
+ The name of the operator to be defined. See above for allowable
+ characters. The name may be schema-qualified, for example
+ <literal>CREATE OPERATOR myschema.+ (...)</>. If not, then
+ the operator is created in the current schema. Two operators
+ in the same schema can have the same name if they operate on
+ different data types. This is called
+ <firstterm>overloading</>.
</para>
</listitem>
</varlistentry>
+
<varlistentry>
- <term><replaceable class="parameter">func_name</replaceable></term>
+ <term><replaceable class="parameter">funcname</replaceable></term>
<listitem>
<para>
The function used to implement this operator.
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">lefttype</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">righttype</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">com_op</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">neg_op</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">res_proc</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">join_proc</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
- <term>HASHES</term>
+ <term><literal>HASHES</literal></term>
<listitem>
<para>
Indicates this operator can support a hash join.
</para>
</listitem>
</varlistentry>
+
<varlistentry>
- <term>MERGES</term>
+ <term><literal>MERGES</literal></term>
<listitem>
<para>
Indicates this operator can support a merge join.
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">left_sort_op</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">right_sort_op</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">less_than_op</replaceable></term>
<listitem>
</para>
</listitem>
</varlistentry>
+
<varlistentry>
<term><replaceable class="parameter">greater_than_op</replaceable></term>
<listitem>
</listitem>
</varlistentry>
</variablelist>
- </para>
- </refsect2>
-
- <refsect2 id="R2-SQL-CREATEOPERATOR-2">
- <refsect2info>
- <date>2000-03-25</date>
- </refsect2info>
- <title>
- Outputs
- </title>
- <para>
- <variablelist>
- <varlistentry>
- <term><computeroutput>
-CREATE OPERATOR
- </computeroutput></term>
- <listitem>
- <para>
- Message returned if the operator is successfully created.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </para>
- </refsect2>
- </refsynopsisdiv>
- <refsect1 id="R1-SQL-CREATEOPERATOR-1">
- <refsect1info>
- <date>2000-03-25</date>
- </refsect1info>
- <title>
- Description
- </title>
- <para>
- <command>CREATE OPERATOR</command> defines a new operator,
- <replaceable class="parameter">name</replaceable>.
- The user who defines an operator becomes its owner.
- </para>
<para>
- If a schema name is given then the operator 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()</>).
- </para>
- <para>
- Two operators in the same schema can have the same name if they operate on
- different data types. This is called <firstterm>overloading</>. The
- system will attempt to pick the intended operator based on the actual
- input data types when there is ambiguity.
+ To give a schema-qualified operator name in <replaceable
+ class="parameter">com_op</replaceable> or the other optional
+ arguments, use the <literal>OPERATOR()</> syntax, for example
+<programlisting>
+COMMUTATOR = OPERATOR(myschema.===) ,
+</programlisting>
</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
<para>
- The operator <replaceable class="parameter">name</replaceable>
- is a sequence of up to <symbol>NAMEDATALEN</>-1 (31 by default) characters
- from the following list:
- <literallayout>
-+ - * / < > = ~ ! @ # % ^ & | ` ? $
- </literallayout>
-
- There are a few restrictions on your choice of name:
- <itemizedlist>
- <listitem>
- <para>
- <literal>$</literal> cannot be defined as a single-character operator,
- although it can be part of a multicharacter operator name.
- </para>
- </listitem>
- <listitem>
- <para>
- <literal>--</literal> and <literal>/*</literal> cannot appear anywhere in an operator name,
- since they will be taken as the start of a comment.
- </para>
- </listitem>
- <listitem>
- <para>
- A multicharacter operator name cannot end in <literal>+</literal> or
- <literal>-</literal>,
- unless the name also contains at least one of these characters:
- <literallayout>
-~ ! @ # % ^ & | ` ? $
- </literallayout>
- For example, <literal>@-</literal> is an allowed operator name,
- but <literal>*-</literal> is not.
- This restriction allows <productname>PostgreSQL</productname> to
- parse SQL-compliant queries without requiring spaces between tokens.
- </para>
- </listitem>
- </itemizedlist>
-
- <note>
- <para>
- When working with non-SQL-standard operator names, you will usually
- need to separate adjacent operators with spaces to avoid ambiguity.
- For example, if you have defined a left-unary operator named <literal>@</literal>,
- you cannot write <literal>X*@Y</literal>; you must write
- <literal>X* @Y</literal> to ensure that
- <productname>PostgreSQL</productname> reads it as two operator names
- not one.
- </para>
- </note>
- </para>
- <para>
- The operator <literal>!=</literal> is mapped to <literal><></literal> on input, so these two names
- are always equivalent.
- </para>
- <para>
- At least one of LEFTARG and RIGHTARG must be defined. For
- binary operators, both should be defined. For right unary
- operators, only LEFTARG should be defined, while for left
- unary operators only RIGHTARG should be defined.
- </para>
- <para>
- The
- <replaceable class="parameter">func_name</replaceable> procedure must have
- been previously defined using <command>CREATE FUNCTION</command> and must
- be defined to accept the correct number of arguments
- (either one or two) of the indicated types.
- </para>
- <para>
- The commutator operator should be identified if one exists,
- so that <productname>PostgreSQL</productname> can
- reverse the order of the operands if it wishes.
- For example, the operator area-less-than, <<<,
- would probably have a commutator
- operator, area-greater-than, >>>.
- Hence, the query optimizer could freely convert:
-
- <programlisting>
-box '((0,0), (1,1))' >>> MYBOXES.description
- </programlisting>
-
- to
-
- <programlisting>
-MYBOXES.description <<< box '((0,0), (1,1))'
- </programlisting>
- </para>
- <para>
- This allows the execution code to always use the latter
- representation and simplifies the query optimizer somewhat.
- </para>
- <para>
- Similarly, if there is a negator operator then it should be
- identified.
- Suppose that an
- operator, area-equal, ===, exists, as well as an area not
- equal, !==.
- The negator link allows the query optimizer to simplify
- <programlisting>
-NOT MYBOXES.description === box '((0,0), (1,1))'
- </programlisting>
- to
- <programlisting>
-MYBOXES.description !== box '((0,0), (1,1))'
- </programlisting>
- </para>
- <para>
- If a commutator operator name is supplied,
- <productname>PostgreSQL</productname>
- searches for it in the catalog. If it is found and it
- does not yet have a commutator itself, then the commutator's
- entry is updated to have the newly created operator as its
- commutator. This applies to the negator, as well.
- This is to allow the definition of two operators that are
- the commutators or the negators of each other. The first
- operator should be defined without a commutator or negator
- (as appropriate). When the second operator is defined,
- name the first as the commutator or negator. The first
- will be updated as a side effect. (As of
- <application>PostgreSQL</application> <literal>6.5</literal>,
- it also works to just have both operators refer to each other.)
- </para>
- <para>
- The HASHES, MERGES, SORT1, SORT2, LTCMP, and GTCMP options are present to
- support the query optimizer in performing joins.
- <productname>PostgreSQL</productname> can always evaluate a join (i.e.,
- processing a clause with two tuple variables separated by an operator that
- returns a <type>boolean</type>) by iterative substitution [WONG76]. In
- addition, <productname>PostgreSQL</productname> can use a hash-join
- algorithm along the lines of [SHAP86]; however, it must know whether this
- strategy is applicable. The current hash-join algorithm is only correct
- for operators that represent equality tests; furthermore, equality of the
- data type must mean bitwise equality of the representation of the type.
- (For example, a data type that contains unused bits that don't matter for
- equality tests could not be hash-joined.) The HASHES flag indicates to the
- query optimizer that a hash join may safely be used with this
- operator.
- </para>
- <para>
- Similarly, the MERGES flag indicates whether merge-sort is a usable join
- strategy for this operator. A merge join requires that the two input
- datatypes have consistent orderings, and that the mergejoin operator
- behave like equality with respect to that ordering. For example, it is
- possible to merge-join equality between an integer and a float variable by
- sorting both inputs in ordinary
- numeric order. Execution of a merge join requires that the system be
- able to identify four operators related to the mergejoin equality operator:
- less-than comparison for the left input datatype,
- less-than comparison for the right input datatype,
- less-than comparison between the two datatypes, and
- greater-than comparison between the two datatypes. It is possible to
- specify these by name, as the SORT1, SORT2, LTCMP, and GTCMP options
- respectively. The system will fill in the default names <literal><</>,
- <literal><</>, <literal><</>, <literal>></> respectively if
- any of these are omitted when MERGES is specified. Also, MERGES will
- be assumed to be implied if any of these four operator options appear.
- </para>
- <para>
- If other join strategies are found to be practical,
- <productname>PostgreSQL</productname>
- will change the optimizer and run-time system to use
- them and will require additional specification when an
- operator is defined. Fortunately, the research community
- invents new join strategies infrequently, and the added
- generality of user-defined join strategies was not felt to
- be worth the complexity involved.
- </para>
- <para>
- The RESTRICT and JOIN options assist the query optimizer in estimating
- result sizes. If a clause of the form:
- <programlisting>
-MYBOXES.description <<< box '((0,0), (1,1))'
- </programlisting>
- is present in the qualification,
- then <productname>PostgreSQL</productname> may have to
- estimate the fraction of the instances in MYBOXES that
- satisfy the clause. The function
- <replaceable class="parameter">res_proc</replaceable>
- must be a registered function (meaning it is already defined using
- <command>CREATE FUNCTION</command>) which accepts arguments of the correct
- data types and returns a floating-point number. The
- query optimizer simply calls this function, passing the
- parameter <literal>((0,0), (1,1))</literal> and multiplies the result by the relation
- size to get the expected number of instances.
- </para>
- <para>
- Similarly, when the operands of the operator both contain
- instance variables, the query optimizer must estimate the
- size of the resulting join. The function join_proc will
- return another floating-point number which will be multiplied
- by the cardinalities of the two tables involved to
- compute the expected result size.
+ Refer to <xref linkend="xoper"> for further information.
</para>
+
<para>
- The difference between the function
- <programlisting>
-my_procedure_1 (MYBOXES.description, box '((0,0), (1,1))')
- </programlisting>
- and the operator
- <programlisting>
-MYBOXES.description === box '((0,0), (1,1))'
- </programlisting>
- is that <productname>PostgreSQL</productname>
- attempts to optimize operators and can
- decide to use an index to restrict the search space when
- operators are involved. However, there is no attempt to
- optimize functions, and they are performed by brute force.
- Moreover, functions can have any number of arguments while
- operators are restricted to one or two.
+ Use <command>DROP OPERATOR</command> to delete user-defined
+ operators from a database.
</para>
-
- <refsect2 id="R2-SQL-CREATEOPERATOR-3">
- <refsect2info>
- <date>2000-03-25</date>
- </refsect2info>
- <title>
- Notes
- </title>
- <para>
- Refer to the chapter on operators in the
- <citetitle>PostgreSQL User's Guide</citetitle>
- for further information.
- Refer to <command>DROP OPERATOR</command> to delete
- user-defined operators from a database.
- </para>
-
- <para>
- To give a schema-qualified operator name in <replaceable
- class="parameter">com_op</replaceable> or the other optional
- arguments, use the <literal>OPERATOR()</> syntax, for example
-<programlisting>
- COMMUTATOR = OPERATOR(myschema.===) ,
-</programlisting>
- </para>
- </refsect2>
</refsect1>
- <refsect1 id="R1-SQL-CREATEOPERATOR-2">
- <title>
- Usage
- </title>
- <para>The following command defines a new operator,
- area-equality, for the BOX data type:
- </para>
- <programlisting>
+ <refsect1>
+ <title>Examples</title>
+
+ <para>
+ The following command defines a new operator, area-equality, for
+ the data type <type>box</type>:
+<programlisting>
CREATE OPERATOR === (
- LEFTARG = box,
- RIGHTARG = box,
- PROCEDURE = area_equal_procedure,
- COMMUTATOR = ===,
- NEGATOR = !==,
- RESTRICT = area_restriction_procedure,
- JOIN = area_join_procedure,
- HASHES,
- SORT1 = <<<,
- SORT2 = <<<
- -- Since sort operators were given, MERGES is implied.
- -- LTCMP and GTCMP are assumed to be < and > respectively
+ LEFTARG = box,
+ RIGHTARG = box,
+ PROCEDURE = area_equal_procedure,
+ COMMUTATOR = ===,
+ NEGATOR = !==,
+ RESTRICT = area_restriction_procedure,
+ JOIN = area_join_procedure,
+ HASHES,
+ SORT1 = <<<,
+ SORT2 = <<<
+ -- Since sort operators were given, MERGES is implied.
+ -- LTCMP and GTCMP are assumed to be < and > respectively
);
- </programlisting>
+</programlisting>
+ </para>
</refsect1>
- <refsect1 id="R1-SQL-CREATEOPERATOR-3">
- <title>
- Compatibility
- </title>
-
- <refsect2 id="R2-SQL-CREATEOPERATOR-4">
- <refsect2info>
- <date>2000-03-25</date>
- </refsect2info>
- <title>
- SQL92
- </title>
-
- <para>
- <command>CREATE OPERATOR</command>
- is a <productname>PostgreSQL</productname> extension.
- There is no <command>CREATE OPERATOR</command>
- statement in <acronym>SQL92</acronym>.
- </para>
- </refsect2>
+ <refsect1>
+ <title>Compatibility</title>
+
+ <para>
+ <command>CREATE OPERATOR</command> is a
+ <productname>PostgreSQL</productname> extension. There are no
+ provisions for user-defined operators in the SQL standard.
+ </para>
</refsect1>
</refentry>
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