The MONTHS_BETWEEN function returns an estimate of the number of months between expression1 and expression2.

The schema is SYSIBM.

expression1 or expression2

Expressions that return a value of either a DATE or TIMESTAMPdata type.

If expression1 represents a date that is later than expression2, the result is positive.
If expression1 represents a date that is earlier than expression2, the result is negative.

• If expression1 and expression2 represent dates or timestamps with the same day of the month, or both arguments represent the last day of their respective months, the result is a the whole number difference based on the year and month values ignoring any time portions of timestamp arguments.
• Otherwise, the whole number part of the result is the difference based on the year and month values.
  The fractional part of the result is calculated from the remainder based on an assumption that every month has 31 days.
  If either argument represents a timestamp, the arguments are effectively processed as timestamps with maximum precision, and the time portions of these values are also considered when determining the result.

The result of the function is a DECIMAL(31,15).
If either argument can be null, the result can be null.
If either argument is null, the result is the null value.

Examples

1. Calculate the number of months that project AD3100 will take.
   Assume that the start date is 1982-01-01 and the end date is 1983-02-01.

          SELECT MONTHS_BETWEEN (PRENDATE, PRSDATE)  
          FROM   PROJECT
          WHERE  PROJNO='AD3100' 

   The result is 13.000000000000000.

2. Here are some additional examples to consider:
   Table 1. Additional examples using MONTHS_BETWEEN
   
   

   Value for argument e1	Value for argument e2	Value returned by MONTHS_BETWEEN (e1,e2)	Value returned by ROUND (MONTHS_BETWEEN (e1,e2)*31,2)	Comment
   2005-02-02	2005-01-01	1.032258064516129	32.00
   2007-11-01-09.00.00.00000	2007-12-07-14.30.12.12345	-1.200945386592741	-37.23
   2007-12-13-09.40.30.00000	2007-11-13-08.40.30.00000	1.000000000000000	31.00	See Note 1
   2007-03-15	2007-02-20	0.838709677419354	26.00	See Note 2
   2008-02-29	2008-02-28-12.00.00	0.016129032258064	0.50
   2008-03-29	2008-02-29	1.000000000000000	31.00
   2008-03-30	2008-02-29	1.032258064516129	32.00
   2008-03-31	2008-02-29	1.000000000000000	31.00	See Note 3

   Note:

   1. The time difference is ignored because the day of the month is the same for both values.
   2. The result is not 23 because, even though February has 28 days, the assumption is that all months have 31 days.
   3. The result is not 33 because both dates are the last day of their respective month, and so the result is only based on the year and month portions.