/*
 * 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(self, column_number)
    VALUE self, 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);
}