How To Replace Values In Different Columns At The Same Time

HI,

I AM HAVING A TABLE WHICH HAS INCREMENTAL COLUMNS,WHERE COLUMNS GETS ADDED EVERY MONTH TO THE TABLE AND THE TABLE THEN CONTAINS PREVIOUS MONTH AND PRESENT MONTH DATA ABOUT CUSTOMERS ,DETAILS AND TRANSACTIONS.
THE PROBLEM WITH THIS DATA IS ,IF THE CUSTOMER IS NEW ,THEN IN PREVIOUS MONTHS HIS INFORMATION IS NULL,WHICH HAVE TO BE CODED HAS "NOT PRESENT".

NOW,
HOW DO WE CONVERT ALL THE PREVIOUS COLUMNS FOR A PARTICULAR CUSTOMER HAS NULL AT THE SAME TIME ?.

HERE IS HOW THE PROC WRITTENED FOR IT GOES :-


DROP PROCEDURE DE_NAT
CREATE PROCEDURE DE_NAT
AS
BEGIN
DECLARE @MONMIN1 NVARCHAR(100),MON NVARCHAR(100),@YEAR NVARCHAR(100) , @MONYEAR NVARCHAR(100)
SET @MONMIN1 = DATENAME((MONTH),DATEADD(MONTH,-1,GETDATE()))
SET @MON = MONTH(GETDATE())
SET @YEAR = YEAR(GETDATE())
SET @MONYEAR = @MON + @YEAR

EXEC('select A.CUSTOMERS,B.*,CAST(A.RFM_40D AS FLOAT) AS R40
INTO TSD_' + @MONYEAR
+ ' from TSD_20 A
LEFT OUTER JOIN SD20 ' + @MONMIN1 + ' B
ON A.CUSTOMERS = B.CUSTOMER')
END


THIS PROC JUST ADDS THE PRESENT MONTHS DATA TILL LAST MONTHS DATA.

BUT IF A CUSTOMER IS NEW, THEN HOW DO I REPLACE THE NULL VALUES FOR THE PREVIOUS DATA TO 'NOT PRESENT'

FOR EG :- IF THERE IS A NEW CUSTOMER ,HOW DO WE CHANGE :-

CUSTOMERS ERTYYTRE RTYUUYTR TYUIIUYT QWERREWQ DFGHHGFD
----------- ---------- ---------- ---------- ----------- ----------
101023 <NULL> <NULL> <NULL> <NULL> 1.0
102022 1.0 1.62.3 3.4 4.5


NOW, AS YOU CAN SEE, THAT FOR CUSTOMERS = '101023'.
THE COLUMN DFGHHGFD IS, THIS MONTHS DATA , I WANT TO CHANGE ALL NULL VALUES PRESIDING IT AS "INACTIVE"

CAN I CHANGE , ALL COLUMNS FROM NULL TO "INACTIVE" , AT THE SAME TIME. ?


AS NEXT MONTH, AGAIN THE COLUMNS IS GONNA INCREASE WHICH WILL
AGAIN CAUSE A PROBLEM .

PLS TELL ME A METHOD , SO THAT I CAN DO THE NEEDFUL.