ftable (PGresult)

    /*
     * call-seq:
     *    res.ftable( column_number ) -> Fixnum
     *
     * Returns the Oid of the table from which the column _column_number_
     * was fetched.
     *
     * Raises ArgumentError if _column_number_ is out of range or if
     * the Oid is undefined for that column.
     */
    static VALUE
    pgresult_ftable(VALUE self, VALUE column_number)
    {
            Oid n = PQftable(get_pgresult(self), NUM2INT(column_number));
            if (n == InvalidOid) {
                    rb_raise(rb_eArgError,"Oid is undefined for column: %d",
                            NUM2INT(column_number));
            }
            return INT2FIX(n);
    }