How to get First day of a month in SQL SERVER 2012 (FOMONTH)

“How to calculate the first date of the current, previous & next month” ? I have seen this question many times in different blogs and there are multiple approaches that we have been following to find it.

For Example

--SQL Server 2005/2008
DECLARE @DATE DATETIME
SET @DATE='2012-09-10'

--First date of the Previous Month
SELECT CONVERT(VARCHAR(10),DATEADD(MONTH, DATEDIFF(MONTH,0,@DATE)-1,0),120) AS [Previous Month]

--First date of the Current Month
SELECT CONVERT(VARCHAR(10),DATEADD(MONTH, DATEDIFF(MONTH,0,@DATE),0),120) AS [Current Month]

--First date of the Next Month
SELECT CONVERT(VARCHAR(10),DATEADD(MONTH, DATEDIFF(MONTH,0,@DATE)+1,0),120) AS [Next Month]

Previous Month
--------------
2012-08-01

(1 row(s) affected)

Current Month
-------------
2012-09-01

(1 row(s) affected)

Next Month
----------
2012-10-01

(1 row(s) affected)

In SQL Server 2012, we can calculate it with the help of a new built in function namely EOMONTH.

Example-1 :
In this example, I calculated the last date of the previous month and later added one more day to it to make the first day of the current month.

Declare @Date as varchar(10) ='2012-09-10'

--First date of the Current Month
Select DateAdd(day,1,EOMONTH(Getdate(),-1)) as [Current Month]

Current Month
-------------
2012-09-01

(1 row(s) affected)

Example-2 : FOMONTH
In this example, we will create a function FOMONTH and will use it same as EOMONTH in SQL server 2012.

CREATE Function [dbo].[FOMONTH]
(@start_date date, @month_to_add int=0)
	Returns Date
AS
BEGIN
	RETURN DATEADD(DAY,1,EOMONTH(@start_date,@month_to_add-1))
END
GO
--First day of the Previous Month
Select dbo.[FOMONTH] (Getdate(),-1)  AS [Previous Month]

--First day of the Current Month
Select dbo.[FOMONTH] ('2012-09-10',0) AS [Current Month]

--First day of the Next Month
Select dbo.[FOMONTH] (Getdate(),1)  AS [Next Month]

--First day of the Current Month WITH DEFAULT VALUE
Select dbo.[FOMONTH] (Getdate(),DEFAULT)  AS [Current Month]

Previous Month
--------------
2012-08-01

(1 row(s) affected)

Current Month
-------------
2012-09-01

(1 row(s) affected)

Next Month
----------
2012-10-01

(1 row(s) affected)

Current Month
-------------
2012-09-01

(1 row(s) affected)