doc/src/sgml/ref/create_operator.sgml

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   2 $PostgreSQL$
   3 PostgreSQL documentation
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   5
   6 <refentry id="SQL-CREATEOPERATOR">
   7  <refmeta>
   8   <refentrytitle id="sql-createoperator-title">CREATE OPERATOR</refentrytitle>
   9   <refmiscinfo>SQL - Language Statements</refmiscinfo>
  10  </refmeta>
  11
  12  <refnamediv>
  13   <refname>CREATE OPERATOR</refname>
  14   <refpurpose>define a new operator</refpurpose>
  15  </refnamediv>
  16
  17  <indexterm zone="sql-createoperator">
  18   <primary>CREATE OPERATOR</primary>
  19  </indexterm>
  20
  21  <refsynopsisdiv>
  22 <synopsis>
  23 CREATE OPERATOR <replaceable>name</replaceable> (
  24     PROCEDURE = <replaceable class="parameter">funcname</replaceable>
  25     [, LEFTARG = <replaceable class="parameter">lefttype</replaceable> ] [, RIGHTARG = <replaceable class="parameter">righttype</replaceable> ]
  26     [, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ] [, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ]
  27     [, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ] [, JOIN = <replaceable class="parameter">join_proc</replaceable> ]
  28     [, HASHES ] [, MERGES ]
  29 )
  30 </synopsis>
  31  </refsynopsisdiv>
  32
  33  <refsect1>
  34   <title>Description</title>
  35
  36   <para>
  37    <command>CREATE OPERATOR</command> defines a new operator,
  38    <replaceable class="parameter">name</replaceable>.  The user who
  39    defines an operator becomes its owner.  If a schema name is given
  40    then the operator is created in the specified schema.  Otherwise it
  41    is created in the current schema.
  42   </para>
  43
  44   <para>
  45    The operator name is a sequence of up to <symbol>NAMEDATALEN</>-1
  46    (63 by default) characters from the following list:
  47 <literallayout>
  48 + - * / &lt; &gt; = ~ ! @ # % ^ &amp; | ` ?
  49 </literallayout>
  50
  51    There are a few restrictions on your choice of name:
  52    <itemizedlist>
  53     <listitem>
  54      <para>
  55      <literal>--</literal> and <literal>/*</literal> cannot appear anywhere in an operator name,
  56      since they will be taken as the start of a comment.
  57      </para>
  58     </listitem>
  59     <listitem>
  60      <para>
  61      A multicharacter operator name cannot end in <literal>+</literal> or
  62      <literal>-</literal>,
  63      unless the name also contains at least one of these characters:
  64 <literallayout>
  65 ~ ! @ # % ^ &amp; | ` ?
  66 </literallayout>
  67      For example, <literal>@-</literal> is an allowed operator name,
  68      but <literal>*-</literal> is not.
  69      This restriction allows <productname>PostgreSQL</productname> to
  70      parse SQL-compliant commands without requiring spaces between tokens.
  71      </para>
  72     </listitem>
  73    </itemizedlist>
  74   </para>
  75
  76   <para>
  77    The operator <literal>!=</literal> is mapped to
  78    <literal>&lt;&gt;</literal> on input, so these two names are always
  79    equivalent.
  80   </para>
  81
  82   <para>
  83    At least one of <literal>LEFTARG</> and <literal>RIGHTARG</> must be defined.  For
  84    binary operators, both must be defined. For right  unary
  85    operators, only <literal>LEFTARG</> should be defined, while for left
  86    unary operators only <literal>RIGHTARG</> should be defined.
  87   </para>
  88
  89   <para>
  90    The <replaceable class="parameter">funcname</replaceable>
  91    procedure must have been previously defined using <command>CREATE
  92    FUNCTION</command> and must be defined to accept the correct number
  93    of arguments (either one or two) of the indicated types.
  94   </para>
  95
  96   <para>
  97    The other clauses specify optional operator optimization clauses.
  98    Their meaning is detailed in <xref linkend="xoper-optimization">.
  99   </para>
 100  </refsect1>
 101
 102  <refsect1>
 103   <title>Parameters</title>
 104
 105     <variablelist>
 106      <varlistentry>
 107       <term><replaceable class="parameter">name</replaceable></term>
 108       <listitem>
 109        <para>
 110         The name of the operator to be defined. See above for allowable
 111         characters.  The name can be schema-qualified, for example
 112         <literal>CREATE OPERATOR myschema.+ (...)</>.  If not, then
 113         the operator is created in the current schema.  Two operators
 114         in the same schema can have the same name if they operate on
 115         different data types.  This is called
 116         <firstterm>overloading</>.
 117        </para>
 118       </listitem>
 119      </varlistentry>
 120
 121      <varlistentry>
 122       <term><replaceable class="parameter">funcname</replaceable></term>
 123       <listitem>
 124        <para>
 125         The function used to implement this operator.
 126        </para>
 127       </listitem>
 128      </varlistentry>
 129
 130      <varlistentry>
 131       <term><replaceable class="parameter">lefttype</replaceable></term>
 132       <listitem>
 133        <para>
 134         The data type of the operator's left operand, if any.
 135         This option would be omitted for a left-unary operator.
 136        </para>
 137       </listitem>
 138      </varlistentry>
 139
 140      <varlistentry>
 141       <term><replaceable class="parameter">righttype</replaceable></term>
 142       <listitem>
 143        <para>
 144         The data type of the operator's right operand, if any.
 145         This option would be omitted for a right-unary operator.
 146        </para>
 147       </listitem>
 148      </varlistentry>
 149
 150      <varlistentry>
 151       <term><replaceable class="parameter">com_op</replaceable></term>
 152       <listitem>
 153        <para>
 154         The commutator of this operator.
 155        </para>
 156       </listitem>
 157      </varlistentry>
 158
 159      <varlistentry>
 160       <term><replaceable class="parameter">neg_op</replaceable></term>
 161       <listitem>
 162        <para>
 163         The negator of this operator.
 164        </para>
 165       </listitem>
 166      </varlistentry>
 167
 168      <varlistentry>
 169       <term><replaceable class="parameter">res_proc</replaceable></term>
 170       <listitem>
 171        <para>
 172         The restriction selectivity estimator function for this operator.
 173        </para>
 174       </listitem>
 175      </varlistentry>
 176
 177      <varlistentry>
 178       <term><replaceable class="parameter">join_proc</replaceable></term>
 179       <listitem>
 180        <para>
 181         The join selectivity estimator function for this operator.
 182        </para>
 183       </listitem>
 184      </varlistentry>
 185
 186      <varlistentry>
 187       <term><literal>HASHES</literal></term>
 188       <listitem>
 189        <para>
 190        Indicates this operator can support a hash join.
 191        </para>
 192       </listitem>
 193      </varlistentry>
 194
 195      <varlistentry>
 196       <term><literal>MERGES</literal></term>
 197       <listitem>
 198        <para>
 199        Indicates this operator can support a merge join.
 200        </para>
 201       </listitem>
 202      </varlistentry>
 203     </variablelist>
 204
 205   <para>
 206    To give a schema-qualified operator name in <replaceable
 207    class="parameter">com_op</replaceable> or the other optional
 208    arguments, use the <literal>OPERATOR()</> syntax, for example:
 209 <programlisting>
 210 COMMUTATOR = OPERATOR(myschema.===) ,
 211 </programlisting>
 212   </para>
 213  </refsect1>
 214
 215  <refsect1>
 216   <title>Notes</title>
 217
 218   <para>
 219    Refer to <xref linkend="xoper"> for further information.
 220   </para>
 221
 222   <para>
 223    The obsolete options <literal>SORT1</>, <literal>SORT2</>,
 224    <literal>LTCMP</>, and <literal>GTCMP</> were formerly used to
 225    specify the names of sort operators associated with a merge-joinable
 226    operator.  This is no longer necessary, since information about
 227    associated operators is found by looking at B-tree operator families
 228    instead.  If one of these options is given, it is ignored except
 229    for implicitly setting <literal>MERGES</> true.
 230   </para>
 231
 232   <para>
 233    Use <xref linkend="sql-dropoperator"
 234    endterm="sql-dropoperator-title"> to delete user-defined operators
 235    from a database.  Use <xref linkend="sql-alteroperator"
 236    endterm="sql-alteroperator-title"> to modify operators in a
 237    database.
 238   </para>
 239  </refsect1>
 240
 241  <refsect1>
 242   <title>Examples</title>
 243
 244   <para>
 245    The following command defines a new operator, area-equality, for
 246    the data type <type>box</type>:
 247 <programlisting>
 248 CREATE OPERATOR === (
 249     LEFTARG = box,
 250     RIGHTARG = box,
 251     PROCEDURE = area_equal_procedure,
 252     COMMUTATOR = ===,
 253     NEGATOR = !==,
 254     RESTRICT = area_restriction_procedure,
 255     JOIN = area_join_procedure,
 256     HASHES, MERGES
 257 );
 258 </programlisting>
 259   </para>
 260  </refsect1>
 261
 262  <refsect1>
 263   <title>Compatibility</title>
 264
 265   <para>
 266    <command>CREATE OPERATOR</command> is a
 267    <productname>PostgreSQL</productname> extension.  There are no
 268    provisions for user-defined operators in the SQL standard.
 269   </para>
 270  </refsect1>
 271
 272  <refsect1>
 273   <title>See Also</title>
 274
 275   <simplelist type="inline">
 276    <member><xref linkend="sql-alteroperator" endterm="sql-alteroperator-title"></member>
 277    <member><xref linkend="sql-createopclass" endterm="sql-createopclass-title"></member>
 278    <member><xref linkend="sql-dropoperator" endterm="sql-dropoperator-title"></member>
 279   </simplelist>
 280  </refsect1>
 281 </refentry>