</varlistentry>
        </variablelist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_relation</structfield></term>
      <listitem>
       <para>
        A pointer to a structure describing the relation that the trigger fired for.
        Look at <filename>utils/rel.h</filename> for details about
        this structure.  The most interesting things are
        <literal>tg_relation-&gt;rd_att</literal> (descriptor of the relation
        tuples) and <literal>tg_relation-&gt;rd_rel-&gt;relname</literal>
        (relation name; the type is not <type>char*</type> but
        <type>NameData</type>; use
        <literal>SPI_getrelname(tg_relation)</literal> to get a <type>char*</type> if you
        need a copy of the name).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_trigtuple</structfield></term>
      <listitem>
       <para>
        A pointer to the row for which the trigger was fired. This is
        the row being inserted, updated, or deleted.  If this trigger
        was fired for an <command>INSERT</command> or
        <command>DELETE</command> then this is what you should return
        from the function if you don't want to replace the row with
        a different one (in the case of <command>INSERT</command>) or
        skip the operation.  For triggers on foreign tables, values of system
        columns herein are unspecified.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_newtuple</structfield></term>
      <listitem>
       <para>
        A pointer to the new version of the row, if the trigger was
        fired for an <command>UPDATE</command>, and <symbol>NULL</symbol> if
        it is for an <command>INSERT</command> or a
        <command>DELETE</command>. This is what you have to return
        from the function if the event is an <command>UPDATE</command>
        and you don't want to replace this row by a different one or
        skip the operation.  For triggers on foreign tables, values of system
        columns herein are unspecified.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_trigger</structfield></term>
      <listitem>
       <para>
        A pointer to a structure of type <structname>Trigger</structname>,
        defined in <filename>utils/reltrigger.h</filename>:

<programlisting>
typedef struct Trigger
{
    Oid         tgoid;
    char       *tgname;
    Oid         tgfoid;
    int16       tgtype;
    char        tgenabled;
    bool        tgisinternal;
    bool        tgisclone;
    Oid         tgconstrrelid;
    Oid         tgconstrindid;
    Oid         tgconstraint;
    bool        tgdeferrable;
    bool        tginitdeferred;
    int16       tgnargs;
    int16       tgnattr;
    int16      *tgattr;
    char      **tgargs;
    char       *tgqual;
    char       *tgoldtable;
    char       *tgnewtable;
} Trigger;
</programlisting>

       where <structfield>tgname</structfield> is the trigger's name,
       <structfield>tgnargs</structfield> is the number of arguments in
       <structfield>tgargs</structfield>, and <structfield>tgargs</structfield> is an array of
       pointers to the arguments specified in the <command>CREATE
       TRIGGER</command> statement. The other members are for internal use
       only.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_trigslot</structfield></term>
      <listitem>
       <para>
        The slot containing <structfield>tg_trigtuple</structfield>,
        or a <symbol>NULL</symbol> pointer if there is no such tuple.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_newslot</structfield></term>
      <listitem>
       <para>
        The slot containing <structfield>tg_newtuple</structfield>,
        or a <symbol>NULL</symbol>