'本月最后一天 DateSerial(year(date), month(date)+1, 0) '上个月最后一天 DateSerial(year(date), month(date), 0) '上上个月最后一天 DateSerial(year(date), month(date)-1, 0) '本月第一天 DateSerial(year(date), month(date), 1) '上个月第一天 DateSerial(year(date), month(date)-1, 1) '上上个月第一天 DateSerial(year(date), month(date)-2, 1)