doc/src/sgml/ref/create_opclass.sgml

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   2 doc/src/sgml/ref/create_opclass.sgml
   3 PostgreSQL documentation
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   5
   6 <refentry id="sql-createopclass">
   7  <indexterm zone="sql-createopclass">
   8   <primary>CREATE OPERATOR CLASS</primary>
   9  </indexterm>
  10
  11  <refmeta>
  12   <refentrytitle>CREATE OPERATOR CLASS</refentrytitle>
  13   <manvolnum>7</manvolnum>
  14   <refmiscinfo>SQL - Language Statements</refmiscinfo>
  15  </refmeta>
  16
  17  <refnamediv>
  18   <refname>CREATE OPERATOR CLASS</refname>
  19   <refpurpose>define a new operator class</refpurpose>
  20  </refnamediv>
  21
  22  <refsynopsisdiv>
  23 <synopsis>
  24 CREATE OPERATOR CLASS <replaceable class="parameter">name</replaceable> [ DEFAULT ] FOR TYPE <replaceable class="parameter">data_type</replaceable>
  25   USING <replaceable class="parameter">index_method</replaceable> [ FAMILY <replaceable class="parameter">family_name</replaceable> ] AS
  26   {  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> ]
  27    | 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> [, ...] )
  28    | STORAGE <replaceable class="parameter">storage_type</replaceable>
  29   } [, ... ]
  30 </synopsis>
  31  </refsynopsisdiv>
  32
  33  <refsect1>
  34   <title>Description</title>
  35
  36   <para>
  37    <command>CREATE OPERATOR CLASS</command> creates a new operator class.
  38    An operator class defines how a particular data type can be used with
  39    an index.  The operator class specifies that certain operators will fill
  40    particular roles or <quote>strategies</quote> for this data type and this
  41    index method.  The operator class also specifies the support functions to
  42    be used by
  43    the index method when the operator class is selected for an
  44    index column.  All the operators and functions used by an operator
  45    class must be defined before the operator class can be created.
  46   </para>
  47
  48   <para>
  49    If a schema name is given then the operator class is created in the
  50    specified schema.  Otherwise it is created in the current schema.
  51    Two operator classes in the same schema can have the same name only if they
  52    are for different index methods.
  53   </para>
  54
  55   <para>
  56    The user who defines an operator class becomes its owner.  Presently,
  57    the creating user must be a superuser.  (This restriction is made because
  58    an erroneous operator class definition could confuse or even crash the
  59    server.)
  60   </para>
  61
  62   <para>
  63    <command>CREATE OPERATOR CLASS</command> does not presently check
  64    whether the operator class definition includes all the operators and
  65    functions required by the index method, nor whether the operators and
  66    functions form a self-consistent set.  It is the user's
  67    responsibility to define a valid operator class.
  68   </para>
  69
  70   <para>
  71    Related operator classes can be grouped into <firstterm>operator
  72    families</firstterm>.  To add a new operator class to an existing family,
  73    specify the <literal>FAMILY</literal> option in <command>CREATE OPERATOR
  74    CLASS</command>.  Without this option, the new class is placed into
  75    a family named the same as the new class (creating that family if
  76    it doesn't already exist).
  77   </para>
  78
  79   <para>
  80    Refer to <xref linkend="xindex"/> for further information.
  81   </para>
  82  </refsect1>
  83
  84  <refsect1>
  85   <title>Parameters</title>
  86
  87   <variablelist>
  88    <varlistentry>
  89     <term><replaceable class="parameter">name</replaceable></term>
  90     <listitem>
  91      <para>
  92       The name of the operator class to be created.  The name can be
  93       schema-qualified.
  94      </para>
  95     </listitem>
  96    </varlistentry>
  97
  98    <varlistentry>
  99     <term><literal>DEFAULT</literal></term>
 100     <listitem>
 101      <para>
 102       If present, the operator class will become the default
 103       operator class for its data type.  At most one operator class
 104       can be the default for a specific data type and index method.
 105      </para>
 106     </listitem>
 107    </varlistentry>
 108
 109    <varlistentry>
 110     <term><replaceable class="parameter">data_type</replaceable></term>
 111     <listitem>
 112      <para>
 113       The column data type that this operator class is for.
 114      </para>
 115     </listitem>
 116    </varlistentry>
 117
 118    <varlistentry>
 119     <term><replaceable class="parameter">index_method</replaceable></term>
 120     <listitem>
 121      <para>
 122       The name of the index method this operator class is for.
 123      </para>
 124     </listitem>
 125    </varlistentry>
 126
 127    <varlistentry>
 128     <term><replaceable class="parameter">family_name</replaceable></term>
 129     <listitem>
 130      <para>
 131       The name of the existing operator family to add this operator class to.
 132       If not specified, a family named the same as the operator class is
 133       used (creating it, if it doesn't already exist).
 134      </para>
 135     </listitem>
 136    </varlistentry>
 137
 138    <varlistentry>
 139     <term><replaceable class="parameter">strategy_number</replaceable></term>
 140     <listitem>
 141      <para>
 142       The index method's strategy number for an operator
 143       associated with the operator class.
 144      </para>
 145     </listitem>
 146    </varlistentry>
 147
 148    <varlistentry>
 149     <term><replaceable class="parameter">operator_name</replaceable></term>
 150     <listitem>
 151      <para>
 152       The name (optionally schema-qualified) of an operator associated
 153       with the operator class.
 154      </para>
 155     </listitem>
 156    </varlistentry>
 157
 158    <varlistentry>
 159     <term><replaceable class="parameter">op_type</replaceable></term>
 160     <listitem>
 161      <para>
 162       In an <literal>OPERATOR</literal> clause,
 163       the operand data type(s) of the operator, or <literal>NONE</literal> to
 164       signify a prefix operator.  The operand data
 165       types can be omitted in the normal case where they are the same
 166       as the operator class's data type.
 167      </para>
 168
 169      <para>
 170       In a <literal>FUNCTION</literal> clause, the operand data type(s) the
 171       function is intended to support, if different from
 172       the input data type(s) of the function (for B-tree comparison functions
 173       and hash functions)
 174       or the class's data type (for B-tree sort support functions,
 175       B-tree equal image functions, and all functions in GiST,
 176       SP-GiST, GIN and BRIN operator classes).  These defaults are
 177       correct, and so <replaceable
 178        class="parameter">op_type</replaceable> need not be specified
 179       in <literal>FUNCTION</literal> clauses, except for the case of a
 180       B-tree sort support function that is meant to support
 181       cross-data-type comparisons.
 182      </para>
 183     </listitem>
 184    </varlistentry>
 185
 186    <varlistentry>
 187     <term><replaceable class="parameter">sort_family_name</replaceable></term>
 188     <listitem>
 189      <para>
 190       The name (optionally schema-qualified) of an existing <literal>btree</literal> operator
 191       family that describes the sort ordering associated with an ordering
 192       operator.
 193      </para>
 194
 195      <para>
 196       If neither <literal>FOR SEARCH</literal> nor <literal>FOR ORDER BY</literal> is
 197       specified, <literal>FOR SEARCH</literal> is the default.
 198      </para>
 199     </listitem>
 200    </varlistentry>
 201
 202    <varlistentry>
 203     <term><replaceable class="parameter">support_number</replaceable></term>
 204     <listitem>
 205      <para>
 206       The index method's support function number for a
 207       function associated with the operator class.
 208      </para>
 209     </listitem>
 210    </varlistentry>
 211
 212    <varlistentry>
 213     <term><replaceable class="parameter">function_name</replaceable></term>
 214     <listitem>
 215      <para>
 216       The name (optionally schema-qualified) of a function that is an
 217       index method support function for the operator class.
 218      </para>
 219     </listitem>
 220    </varlistentry>
 221
 222    <varlistentry>
 223     <term><replaceable class="parameter">argument_type</replaceable></term>
 224     <listitem>
 225      <para>
 226       The parameter data type(s) of the function.
 227      </para>
 228     </listitem>
 229    </varlistentry>
 230
 231    <varlistentry>
 232     <term><replaceable class="parameter">storage_type</replaceable></term>
 233     <listitem>
 234      <para>
 235       The data type actually stored in the index.  Normally this is
 236       the same as the column data type, but some index methods
 237       (currently GiST, GIN, SP-GiST and BRIN) allow it to be different.  The
 238       <literal>STORAGE</literal> clause must be omitted unless the index
 239       method allows a different type to be used.
 240       If the column <replaceable class="parameter">data_type</replaceable> is specified
 241       as <type>anyarray</type>, the <replaceable class="parameter">storage_type</replaceable>
 242       can be declared as <type>anyelement</type> to indicate that the index
 243       entries are members of the element type belonging to the actual array
 244       type that each particular index is created for.
 245      </para>
 246     </listitem>
 247    </varlistentry>
 248   </variablelist>
 249
 250   <para>
 251    The <literal>OPERATOR</literal>, <literal>FUNCTION</literal>, and <literal>STORAGE</literal>
 252    clauses can appear in any order.
 253   </para>
 254  </refsect1>
 255
 256  <refsect1>
 257   <title>Notes</title>
 258
 259   <para>
 260    Because the index machinery does not check access permissions on functions
 261    before using them, including a function or operator in an operator class
 262    is tantamount to granting public execute permission on it.  This is usually
 263    not an issue for the sorts of functions that are useful in an operator
 264    class.
 265   </para>
 266
 267   <para>
 268    The operators should not be defined by SQL functions.  An SQL function
 269    is likely to be inlined into the calling query, which will prevent
 270    the optimizer from recognizing that the query matches an index.
 271   </para>
 272
 273   <para>
 274    Before <productname>PostgreSQL</productname> 8.4, the <literal>OPERATOR</literal>
 275    clause could include a <literal>RECHECK</literal> option.  This is no longer
 276    supported because whether an index operator is <quote>lossy</quote> is now
 277    determined on-the-fly at run time.  This allows efficient handling of
 278    cases where an operator might or might not be lossy.
 279   </para>
 280  </refsect1>
 281
 282  <refsect1>
 283   <title>Examples</title>
 284
 285   <para>
 286    The following example command defines a GiST index operator class
 287    for the data type <literal>_int4</literal> (array of <type>int4</type>).  See the
 288    <xref linkend="intarray"/> module for the complete example.
 289   </para>
 290
 291 <programlisting>
 292 CREATE OPERATOR CLASS gist__int_ops
 293     DEFAULT FOR TYPE _int4 USING gist AS
 294         OPERATOR        3       &amp;&amp;,
 295         OPERATOR        6       = (anyarray, anyarray),
 296         OPERATOR        7       @&gt;,
 297         OPERATOR        8       &lt;@,
 298         OPERATOR        20      @@ (_int4, query_int),
 299         FUNCTION        1       g_int_consistent (internal, _int4, smallint, oid, internal),
 300         FUNCTION        2       g_int_union (internal, internal),
 301         FUNCTION        3       g_int_compress (internal),
 302         FUNCTION        4       g_int_decompress (internal),
 303         FUNCTION        5       g_int_penalty (internal, internal, internal),
 304         FUNCTION        6       g_int_picksplit (internal, internal),
 305         FUNCTION        7       g_int_same (_int4, _int4, internal);
 306 </programlisting>
 307  </refsect1>
 308
 309  <refsect1>
 310   <title>Compatibility</title>
 311
 312   <para>
 313    <command>CREATE OPERATOR CLASS</command> is a
 314    <productname>PostgreSQL</productname> extension.  There is no
 315    <command>CREATE OPERATOR CLASS</command> statement in the SQL
 316    standard.
 317   </para>
 318  </refsect1>
 319
 320  <refsect1>
 321   <title>See Also</title>
 322
 323   <simplelist type="inline">
 324    <member><xref linkend="sql-alteropclass"/></member>
 325    <member><xref linkend="sql-dropopclass"/></member>
 326    <member><xref linkend="sql-createopfamily"/></member>
 327    <member><xref linkend="sql-alteropfamily"/></member>
 328   </simplelist>
 329  </refsect1>
 330 </refentry>