How to retrieve the last day of the month .... Or Last date in the week ?

Answer:
To add a addendum ... how can I find out the number of days in a given month.
eg. If I were to give you '2003-03-01' I should get 31.
If you feel its a bit tricky in nature then ... See the solutions below ...
DECLARE @Date datetime
SET @Date = '2000/02/1'
SELECT DATEADD(dd,-(DATEPART(dw, @Date) - 1),@Date) AS 'First day of the week'
SELECT DATEADD(dd,-(DATEPART(dw, @Date) - 7),@Date) AS 'Last day of the week'
SELECT DAY(DATEADD(d, -DAY(DATEADD(m,1,@Date)),DATEADD(m,1,@Date))) AS 'Last day of the month'
Since the Last Day would yield you the number of days in a month then it anwers my addendum question also. Some more solutions for the number of days in a month are below:

DECLARE @d DATETIME
SET @d = '2003-02-1'
select datepart(dd, dateadd(dd, -(datepart(dd, dateadd(mm, 1, @d))),dateadd(mm, 1, @d))) AS 'Last day of the month'

GO

DECLARE @d DATETIME
SET @d = '2000-02-1'
SELECT CASE WHEN MONTH(@d) = 1
            THEN 31
            WHEN MONTH(@d) = 2
            THEN CASE WHEN (YEAR(@d) % 4 = 0 AND YEAR(@d) % 100 <> 0) OR
                           YEAR(@d) % 400 = 0
                      THEN 29
                      ELSE 28
            END
            WHEN MONTH(@d) = 3
            THEN 31
            WHEN MONTH(@d) = 4
            THEN 30
            WHEN MONTH(@d) = 5
            THEN 31
            WHEN MONTH(@d) = 6
            THEN 30
            WHEN MONTH(@d) = 7
            THEN 31
            WHEN MONTH(@d) = 8
            THEN 31
            WHEN MONTH(@d) = 9
            THEN 30
            WHEN MONTH(@d) = 10
            THEN 31
            WHEN MONTH(@d) = 11
            THEN 30
            WHEN MONTH(@d) = 12
            THEN 31
       END AS 'Last day of the month'

Whew .... That's a mess to understand ... Believe me they work ... :-) ... There are hundreds of way the SQL Selects can be done ... This is just few of them ... And one more ...

SELECT DAY(DATEADD(DAY,-1,DATEADD(MONTH,1,DATEADD(DAY,1-DAY(@d),@d)))) AS 'Last day of the month'

 

Note: Some of the tips and tricks are subjected to some specific SQL Server settings hence use them with loads of care.