If you are after T-SQL First Day of Previous Month calculation then you are in the right place.
To return first day of previous month using T-SQL we can use the following statement:
Below is a visual representation of the logic I want to use to get first day of previous month and below the picture is the explanation.
1) Our today's date is 20th of Feb. We substract number of days in the month from our date (20) and we get last day of previous month.
2) We add one day to get first day of current month.
3) We go one month back so first day of the month stays the same and Feb changes to Jan.
Now the code:
SELECT DATEADD(m,-1, Dateadd(d,1-DATEPART(d,getdate()),GETDATE())) AS [First Day of Previous Month]
The result of this T-SQL statement is first day of previous month.
Hope that helps!