Because of inconsistencies in the number of days in the months of the year, adding a month to a given date does not always result in the same day of the next month. The result of adding one month to January 31 cannot be February 31. Adding a month to a given date results in the same day of the next month when such a day exists. If it does not exist, adding a month to a given date results in the last day of the next month. For example, if you add one month to January 31, the result is February 28 (or February 29 in a leap year).
To avoid inconsistencies in date arithmetic that is caused by months, use days. For example, to increment a date by the difference between two dates, you can use an SQL statement like this:
SELECT DATE(DAYS('1988-01-05') + DAYS(ENDD) - DAYS(STARTD))
FROM Q.PROJECT
WHERE PROJNO = '1408'
QMF produces this report:
+--------------------------------------------------------------------------------+ | COL1 | | ---------- | | 1989-07-25 | +--------------------------------------------------------------------------------+