Dim QueryMonth As Date = Date.Today '自定义日期
Dim FirstDay As Date = New Date(QueryMonth.Year,QueryMonth.Month,1) '第一天
Dim LastDay As Date = New Date(QueryMonth.Year,QueryMonth.Month,Date.DaysInMonth(QueryMonth.Year,QueryMonth.Month)) '最后一天
Dim sFirstDay As Date = FirstDay.AddMonths(-1) '上月第一天
Dim sLastDay As Date = FirstDay.AddDays(-1) '上月最后一天