First and Last Date of a current and Previous Months

FirstDay_PrevMonth: add_months(last_date(sysdate()), -2) + 1

LastDay_PrevMonth: last_date( add_months(sysdate(),-1))

First day of the current month:add_months(last_date(sysdate()), -1) + 1

Last Day of the current month : last_date(sysdate())