Subtract dates

The result of subtracting one date (DATE2) from another (DATE1) is a date duration that specifies the number of years, months, and days between the two dates.

The data type of the result is DECIMAL(8,0). If DATE1 is greater than or equal to DATE2, DATE2 is subtracted from DATE1. If DATE1 is less than DATE2, however, DATE1 is subtracted from DATE2, and the sign of the result is made negative. The following procedural description clarifies the steps involved in the operation RESULT = DATE1 - DATE2.

If %DAY(DATE2) <= %DAY(DATE1) ;
   then %DAY(RESULT) = %DAY(DATE1) - %DAY(DATE2).

If %DAY(DATE2) > %DAY(DATE1) ;
   then %DAY(RESULT) = N + %DAY(DATE1) - %DAY(DATE2) ;
   where N = the last day of %MONTH(DATE2). ;
   %MONTH(DATE2) is then incremented by 1.

If %MONTH(DATE2) <= %MONTH(DATE1) ;
   then %MONTH(RESULT) = %MONTH(DATE1) - %MONTH(DATE2).

If %MONTH(DATE2) > %MONTH(DATE1) ;
   then %MONTH(RESULT) = 12 + %MONTH(DATE1) - %MONTH(DATE2). ;
   %YEAR(DATE2) is then incremented by 1.

%YEAR(RESULT) = %YEAR(DATE1) - %YEAR(DATE2).

For example, the result of %DATE('3/15/2000') - '12/31/1999' is 215 (or, a duration of 0 years, 2 months, and 15 days).