How to get 1st date of a month ?

In rdfs sql section,you just formate the to_date as fallow:

sql
where to_char(datefield,dd/mm/yyyy)=to_char(to_date,01||/mm/yyyy)

To get the first date of a month, truncate the date to the month, like this:

Code
SELECT trunc(my_date,Mon) FROM dual;

select last_day(add_months(trunc(sysdate),-1)) + 1 from dual;

OR

select trunc(sysdate,MON) from dual;

Select Trunc(SYSDATE,MON) From Dual;