<type>oid</type> would use.  The alias
    types allow simplified lookup of OID values for objects.  For example,
    to examine the <structname>pg_attribute</structname> rows related to a table
    <literal>mytable</literal>, one could write:
<programlisting>
SELECT * FROM pg_attribute WHERE attrelid = 'mytable'::regclass;
</programlisting>
    rather than:
<programlisting>
SELECT * FROM pg_attribute
  WHERE attrelid = (SELECT oid FROM pg_class WHERE relname = 'mytable');
</programlisting>
    While that doesn't look all that bad by itself, it's still oversimplified.
    A far more complicated sub-select would be needed to
    select the right OID if there are multiple tables named
    <literal>mytable</literal> in different schemas.
    The <type>regclass</type> input converter handles the table lookup according
    to the schema path setting, and so it does the <quote>right thing</quote>
    automatically.  Similarly, casting a table's OID to
    <type>regclass</type> is handy for symbolic display of a numeric OID.
   </para>

    <table id="datatype-oid-table">
     <title>Object Identifier Types</title>
     <tgroup cols="4">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>References</entry>
        <entry>Description</entry>
        <entry>Value Example</entry>
       </row>
      </thead>

      <tbody>

       <row>
        <entry><type>oid</type></entry>
        <entry>any</entry>
        <entry>numeric object identifier</entry>
        <entry><literal>564182</literal></entry>
       </row>

       <row>
        <entry><type>regclass</type></entry>
        <entry><structname>pg_class</structname></entry>
        <entry>relation name</entry>
        <entry><literal>pg_type</literal></entry>
       </row>

       <row>
        <entry><type>regcollation</type></entry>
        <entry><structname>pg_collation</structname></entry>
        <entry>collation name</entry>
        <entry><literal>"POSIX"</literal></entry>
       </row>

       <row>
        <entry><type>regconfig</type></entry>
        <entry><structname>pg_ts_config</structname></entry>
        <entry>text search configuration</entry>
        <entry><literal>english</literal></entry>
       </row>

       <row>
        <entry><type>regdictionary</type></entry>
        <entry><structname>pg_ts_dict</structname></entry>
        <entry>text search dictionary</entry>
        <entry><literal>simple</literal></entry>
       </row>

       <row>
        <entry><type>regnamespace</type></entry>
        <entry><structname>pg_namespace</structname></entry>
        <entry>namespace name</entry>
        <entry><literal>pg_catalog</literal></entry>
       </row>

       <row>
        <entry><type>regoper</type></entry>
        <entry><structname>pg_operator</structname></entry>
        <entry>operator name</entry>
        <entry><literal>+</literal></entry>
       </row>

       <row>
        <entry><type>regoperator</type></entry>
        <entry><structname>pg_operator</structname></entry>
        <entry>operator with argument types</entry>
        <entry><literal>*(integer,&zwsp;integer)</literal>
         or <literal>-(NONE,&zwsp;integer)</literal></entry>
       </row>

       <row>
        <entry><type>regproc</type></entry>
        <entry><structname>pg_proc</structname></entry>
        <entry>function name</entry>
        <entry><literal>sum</literal></entry>
       </row>

       <row>
        <entry><type>regprocedure</type></entry>
        <entry><structname>pg_proc</structname></entry>
        <entry>function with argument types</entry>
        <entry><literal>sum(int4)</literal></entry>
       </row>

       <row>
        <entry><type>regrole</type></entry>
        <entry><structname>pg_authid</structname></entry>
        <entry>role name</entry>
        <entry><literal>smithee</literal></entry>
       </row>

       <row>
        <entry><type>regtype</type></entry>
        <entry><structname>pg_type</structname></entry>
        <entry>data