delete from MyTable where Cdate between ('2012-08-01','2012-08-31')

;WITH MyNewData (a,b,c) AS (
    SELECT 1, 2, 3
    UNION ALL SELECT 2, 3, 4
    -- etc. for 28 more records
    UNION ALL SELECT 31, 4, 5)
UPDATE t
SET b=d.b     -- new data for column b
    ,c=d.c       -- new data for column c
FROM MyTable t
INNER JOIN MyNewData d
    ON d.a = t.a

SELECT	DATEADD (DAY,sv.Number,'20120801')
FROM	master.dbo.spt_values sv
WHERE	sv.Name IS NULL AND sv.Number < 31