doc/src/sgml/ref/create_opclass.sgml

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   5
   6 <refentry id="SQL-CREATEOPCLASS">
   7  <refmeta>
   8   <refentrytitle id="sql-createopclass-title">CREATE OPERATOR CLASS</refentrytitle>
   9   <manvolnum>7</manvolnum>
  10   <refmiscinfo>SQL - Language Statements</refmiscinfo>
  11  </refmeta>
  12
  13  <refnamediv>
  14   <refname>CREATE OPERATOR CLASS</refname>
  15   <refpurpose>define a new operator class</refpurpose>
  16  </refnamediv>
  17
  18  <indexterm zone="sql-createopclass">
  19   <primary>CREATE OPERATOR CLASS</primary>
  20  </indexterm>
  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> ) ]
  27    | FUNCTION <replaceable class="parameter">support_number</replaceable> [ ( <replaceable class="parameter">op_type</replaceable> [ , <replaceable class="parameter">op_type</replaceable> ] ) ] <replaceable class="parameter">funcname</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</> for this data type and this
  41    index method.  The operator class also specifies the support procedures 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</>.  To add a new operator class to an existing family,
  73    specify the <literal>FAMILY</> 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</></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</> clause,
 163       the operand data type(s) of the operator, or <literal>NONE</> to
 164       signify a left-unary or right-unary 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</> 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 and hash indexes)
 173       or the class's data type (for GIN and GiST indexes).  These defaults
 174       are always correct, so there is no point in specifying <replaceable
 175       class="parameter">op_type</replaceable> in a <literal>FUNCTION</> clause
 176       in <command>CREATE OPERATOR CLASS</>, but the option is provided
 177       for consistency with the comparable syntax in
 178       <command>ALTER OPERATOR FAMILY</>.
 179      </para>
 180     </listitem>
 181    </varlistentry>
 182
 183    <varlistentry>
 184     <term><replaceable class="parameter">support_number</replaceable></term>
 185     <listitem>
 186      <para>
 187       The index method's support procedure number for a
 188       function associated with the operator class.
 189      </para>
 190     </listitem>
 191    </varlistentry>
 192
 193    <varlistentry>
 194     <term><replaceable class="parameter">funcname</replaceable></term>
 195     <listitem>
 196      <para>
 197       The name (optionally schema-qualified) of a function that is an
 198       index method support procedure for the operator class.
 199      </para>
 200     </listitem>
 201    </varlistentry>
 202
 203    <varlistentry>
 204     <term><replaceable class="parameter">argument_types</replaceable></term>
 205     <listitem>
 206      <para>
 207       The parameter data type(s) of the function.
 208      </para>
 209     </listitem>
 210    </varlistentry>
 211
 212    <varlistentry>
 213     <term><replaceable class="parameter">storage_type</replaceable></term>
 214     <listitem>
 215      <para>
 216       The data type actually stored in the index.  Normally this is
 217       the same as the column data type, but some index methods
 218       (currently GIN and GiST) allow it to be different.  The
 219       <literal>STORAGE</> clause must be omitted unless the index
 220       method allows a different type to be used.
 221      </para>
 222     </listitem>
 223    </varlistentry>
 224   </variablelist>
 225
 226   <para>
 227    The <literal>OPERATOR</>, <literal>FUNCTION</>, and <literal>STORAGE</>
 228    clauses can appear in any order.
 229   </para>
 230  </refsect1>
 231
 232  <refsect1>
 233   <title>Notes</title>
 234
 235   <para>
 236    Because the index machinery does not check access permissions on functions
 237    before using them, including a function or operator in an operator class
 238    is tantamount to granting public execute permission on it.  This is usually
 239    not an issue for the sorts of functions that are useful in an operator
 240    class.
 241   </para>
 242
 243   <para>
 244    The operators should not be defined by SQL functions.  A SQL function
 245    is likely to be inlined into the calling query, which will prevent
 246    the optimizer from recognizing that the query matches an index.
 247   </para>
 248
 249   <para>
 250    Before <productname>PostgreSQL</productname> 8.4, the <literal>OPERATOR</>
 251    clause could include a <literal>RECHECK</> option.  This is no longer
 252    supported because whether an index operator is <quote>lossy</> is now
 253    determined on-the-fly at runtime.  This allows efficient handling of
 254    cases where an operator might or might not be lossy.
 255   </para>
 256  </refsect1>
 257
 258  <refsect1>
 259   <title>Examples</title>
 260
 261   <para>
 262    The following example command defines a GiST index operator class
 263    for the data type <literal>_int4</> (array of <type>int4</type>).  See
 264    <filename>contrib/intarray/</> for the complete example.
 265   </para>
 266
 267 <programlisting>
 268 CREATE OPERATOR CLASS gist__int_ops
 269     DEFAULT FOR TYPE _int4 USING gist AS
 270         OPERATOR        3       &amp;&amp;,
 271         OPERATOR        6       = (anyarray, anyarray),
 272         OPERATOR        7       @&gt;,
 273         OPERATOR        8       &lt;@,
 274         OPERATOR        20      @@ (_int4, query_int),
 275         FUNCTION        1       g_int_consistent (internal, _int4, int, oid, internal),
 276         FUNCTION        2       g_int_union (internal, internal),
 277         FUNCTION        3       g_int_compress (internal),
 278         FUNCTION        4       g_int_decompress (internal),
 279         FUNCTION        5       g_int_penalty (internal, internal, internal),
 280         FUNCTION        6       g_int_picksplit (internal, internal),
 281         FUNCTION        7       g_int_same (_int4, _int4, internal);
 282 </programlisting>
 283  </refsect1>
 284
 285  <refsect1>
 286   <title>Compatibility</title>
 287
 288   <para>
 289    <command>CREATE OPERATOR CLASS</command> is a
 290    <productname>PostgreSQL</productname> extension.  There is no
 291    <command>CREATE OPERATOR CLASS</command> statement in the SQL
 292    standard.
 293   </para>
 294  </refsect1>
 295
 296  <refsect1>
 297   <title>See Also</title>
 298
 299   <simplelist type="inline">
 300    <member><xref linkend="sql-alteropclass" endterm="sql-alteropclass-title"></member>
 301    <member><xref linkend="sql-dropopclass" endterm="sql-dropopclass-title"></member>
 302    <member><xref linkend="sql-createopfamily" endterm="sql-createopfamily-title"></member>
 303    <member><xref linkend="sql-alteropfamily" endterm="sql-alteropfamily-title"></member>
 304   </simplelist>
 305  </refsect1>
 306 </refentry>