MONTHS_BETWEEN

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


>>-MONTHS_BETWEEN--(--expression1--,--expression2--)-----------><

expression1: An expression that returns a value of one of the following built-in data types: a date, a timestamp, a character-string, or a graphic-string.; If expression1 is a character or graphic string, it must not be a CLOB or DBCLOB and its values must be a valid string representation of a date or timestamp. For the valid formats of string representations of dates and timestamps, see String representations of datetime values
expression2: An expression that returns a value of one of the following built-in data types: a date, a timestamp, a character-string, or a graphic-string.; If expression2 is a character or graphic string, it must not be a CLOB or DBCLOB and its values must be a valid string representation of a date or timestamp. For the valid formats of string representations of dates and timestamps, see String representations of datetime values

If expression1 represents a date that is later than expression2, then the result is positive. If expression2 represents a date that is later than expression1, then the result is negative. Start of change

If expression1 and expression2 represent dates with the same day of the month or the last 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

Calculate the months between two dates:

  SELECT MONTHS_BETWEEN('2005-01-17', '2005-02-17')
    FROM SYSIBM.SYSDUMMY1

Returns the value -1.000000000000000

  SELECT MONTHS_BETWEEN('2005-02-20', '2005-01-17')
    FROM SYSIBM.SYSDUMMY1

Returns the value 1.096774193548387

The following table contains additional examples:

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 DECIMAL(ROUND( MONTHS_BETWEEN( e1,e2)*31,2), 15, 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:

The time difference is ignored because the day of the month is the same for both values.
The result is not 23 because, even though February has 28 days, the assumption is that all months have 31 days.
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.