Separate Year and Month Columns Combine into One. How to deal with missing?

[Denali]

Hi,

I have a column contain year information and another column contains month information. I would like to combine these two columns into one.

ID               YEAR             MONTH         Date (this is what I want)

001             2012                  08               08/2012

002             2000                  10               10/2000

003                                       06               06/0000

004             2010                  99               00/2010

005             2009                  88               00/2009

I used below code: 

Date = mdy(Month,1,Year);

format Date mmyys7.;

It worked well when both columns contain information. However, it will show missing if someone only has either year or month data. Is there a way to keep the information as mush as possible?

Note: "blank", "88" or "99" are "missing". In the Date variable, I simply wrote "00"  represents those do not have month info and "0000" for those without year info. Does anyone has better way to keep the missing info in the "Date" variable? 

Thanks in advance!

[novinosrin]

is it ok to have to date(want) as  character var rather than numeric sas date for the reason you have data integrity issues? If yes, it;s a simple if then and catx

[novinosrin]

data have;
input ID               YEAR             MONTH        ;
cards;
001             2012                  08               08/2012
002             2000                  10               10/2000
003               .                     06               06/0000
004             2010                  99               00/2010
005             2009                  88               00/2009
;

data want;
set have;
length want $7;
if missing(year) then year=0;
if not (1<=month<=12) then month=0;
want=catx('/',put(month,z2.),put(year,z4.));
run;