I need to rollup data by month. There are a couple ways to do this. I have a date field. So I can rollup with a to_char(mydate,'YYYYMM') this requires a where clause as followings where to_char(mydate,'YYYYMM') = pSomeMonth; This means I need a function based index to support this. We have alot of data, so where possible, I want to avoid adding more indexes. Is there a way to calculate what the last day of the month is? so I can use a between as follows where myDate between to_date(01-MON-YYYY') and to_date(LASTDAYOFMONTH-MON-YYYY') Since the last day of the month can be 28,29,30,31