How to use this sql query in oracle?

Question

Hi all,
i am using one sql query that is
SELECT @ToDate = '2012-10-03 00:00:00.000'
select @BetweenDate = DATEADD(MM,-1,@ToDate)
select @FromDate = DATEADD(m,DATEDIFF(m,0,@BetweenDate),0)
SELECT @ToDate = DATEADD(month, ((YEAR(@BetweenDate) - 1900) * 12) + MONTH(@BetweenDate), -1)
so @todate value is = '2012-10-03 00:00:00.000'
so in @betweendate value will come 1 month before like '2012-09-03 00:00:00.000'
again in @fromdate value will come like that '2012-09-01 00:00:00.000' means first date of @betweendate
and again @todate value will come like that '2012-09-30 00:00:00.000' means last date of @betweendate
it's happening in sql and i have to use same logic in oracle also.
how to use it??
thanks

Answer 1

declare
todate date:= to_date('2012-10-03 00:00:00','yyyy-mm-dd hh:mi:ss');
betwendate date := add_months(todate,-1);
for datediff / additions you can direct subtract/add two different date variables
like
datediff = betweendate -todate
dateadd := todate+1;