I need a date column for a summary report in order to create relative date filter (previous month).  My date column has all sorts of dates/times in the Date Column and I need it to be grouped and aggregated to the first day of the month to make this work.  

Functions available in Zoho do not work the same as TSQL expressions and where I would normally have an easy time of calculating the first day of the month, I can only work out adding a day to the last day of the previous month, but I can't get this to work.  

How do I calculate the first day of the month for any given date?

Thanks!

Jan