避免复杂的多表关联 SELECTFROM user_files uf, df_money_files dm, cw_charge_record cc WHERE uf.user_no = dm.user_no AND dm.user_no = cc.user_no AND …… AND NOT EXISTS(SELECT …) T。这种查询方式难以优化,随着数据量的增加,性能风险显著上升。