access表中按照某个字段排序，结果集竟少了几条纪录？！

sql如下：with DataModule2.equip_refer_query do
  begin
    close;
    sql.clear;
    sql.add('select equipment_no,order_qty,order_no,earliest_start_date,earliest_end_date,last_start_date,last_end_date');
    sql.add('from masl_equipment_order');
    sql.add('order by equipment_no,earliest_start_date asc');              //此处order by子句记录数减少
    open;
  end;