Months between not returning correct value

Question

Select MOD (RUNC (MONTHS_BETWEEN (TO_DATE (\'28-Mar-2017\', \'DD-MON-YYYY\'),
 TO_DATE (\'28-Feb-2017\', \'DD-MON-YYYY\'))), 12) Months from dual

Why i

Answer 1

Because it is working to its documented specification:

MONTHS_BETWEEN returns number of months between dates date1 and date2. The month and the last day of the month are defined by the parameter NLS_CALENDAR. If date1 is later than date2, then the result is positive. If date1 is earlier than date2, then the result is negative. If date1 and date2 are either the same days of the month or both last days of months, then the result is always an integer. Otherwise Oracle Database calculates the fractional portion of the result based on a 31-day month and considers the difference in time components date1 and date2.

If you have requirements that are different to this then you will need to write your own function.