SQL Query to select first day and last day of month

declare @date datetime, @first datetime, @last datetime
set @date = getdate()
set @first = cast(month(@date) as varchar(2)) + '/1/' + cast(year(@date) as varchar(4))
set @last = dateadd(d, -1, dateadd(m, 1, @first))
select @first, @last

select dateadd(mm,datediff(mm,0,getdate()),0)
select dateadd(ms,-3,dateadd(mm,datediff(mm,0,getdate())+1,0))
select dateadd(ms,- 3,dateadd(mm,0,dateadd(mm,datediff(mm,0,getdate())+1,0)))