If I understand correctly,

DATEDD(&YYMD,'M',1)

will add one month to the &YYMD value.

But what does WebFOCUS consider one month equal to? 30 days? Same day, but prior month?

Just curious.

This message has been edited. Last edited by: <Kathryn Henning>,

It use an internal matrix to reduce (or add) the number of days in a month to go to the previous or the next one without creating an invalid date.

Per example:

DEFINE FILE CAR
MTH1/YYMD=DATEADD('2014/03/31', 'M', -1);
MTH2/YYMD=DATEADD('2014/03/31', 'M', -2);
MTH3/YYMD=DATEADD('2014/03/31', 'M', -3);

MTH4/YYMD=DATEADD('2014/03/25', 'M', -5);

END
TABLE FILE CAR
BY COUNTRY NOPRINT
BY MTH1
BY MTH2
BY MTH3
BY MTH4
WHERE COUNTRY EQ 'FRANCE';
END
-RUN

Is resulting in:

MTH1       MTH2       MTH3       MTH4 
2014/02/28 2014/01/31 2013/12/31 2013/10/25 

The date has to be a "smart date", not a text string, which is what &YYMD, and, any Dialogue Manger value is unless converted:

-SET &MTH_1 = DATECVT(DATEADD(DATECVT(&YYMD,'I8YYMD','YYMD'),'M',+1), 'YYMD', 'I8YYMD');
-TYPE &MTH_1
-EXIT

Was just to show the result of month shift with different input date values.
Was easier, I've been lazy
But true, the input of DATEADD, must be a smartdate.

DEFINE FILE CAR
DTE/YYMD=&YYMD;
DT_1 /YYMD=DATEADD(DTE, 'M', -1);
END
TABLE FILE CAR
PRINT DTE DT_1
BY COUNTRY
WHERE COUNTRY EQ 'FRANCE';
END

ok, so it is not just subtracting 30, for example, which is what I was trying to confirm.

Thank you.

And it's smart enough to take care of the leap years as per below example. (I know I used a text date, but it's just to show )

DEFINE FILE CAR
MTH1/YYMD=DATEADD('2012/03/31', 'M', -1);
END
TABLE FILE CAR
BY COUNTRY NOPRINT
BY MTH1
WHERE COUNTRY EQ 'FRANCE';
END
-RUN

seems to be a theme today. Tom, look up the AYMD and AYM functions, for working with &var dates, adding and subtracting. You'll enjoy knowing about them.