The last day of the month on which the given date is calculated SQL statement

DECLARE @date datetime
Set @date =getdate ()
--the first day of the current month minus the day
Select DATEADD (Day,-1,dateadd (Month,datediff (month,0, @date), 0)) as ' last day of last month '
--Another algorithm for the first day of the current month
Select DATEADD (Day,-1,dateadd (Day,1-datepart (Day, @date), @date)) ' Last day of last month '
Select DATEADD (Day,1-datepart (Day, @date), @date)-1 ' last month '
--another algorithm that cannot use the last day of the current month plus one months, because the current month can be 30 days.
--For example, select DATEADD (month,1, ' 2010-06-30 ')--the result is 2010-07-30, not 2010-07-31,
This is also the month-end algorithm using the first day of next month minus 1 days to calculate the reason
--but if the calculation month is 31 days without this problem
--For example, select DATEADD (month,1, ' 2010-05-31 ')--the result is 2010-06-30
-So the following algorithm is correct,-1 means ' 1899-12-31 00:00:00.000 '--select CONVERT (datetime,-1)
Select DATEADD (Month,datediff (month,-1, @date) -1,-1)
--Another current month algorithm
Select DATEADD (Day,-1,dateadd (Day,1-datepart (Day, @date), @date)) ' Last day of last month '
--Simplifying
Select DATEADD (Day,0-datepart, @date), @date) ' Last day of last month '
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