Oracle中的MONTHS_BETWEEN函数

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Syntax：MONTHS_BETWEEN (date1, date2)  

Purpose：返回两个日期之间的月份数

1.如果date1>date2，则返回一个正数；

2.如果date1<date2，则返回一个负数；

3.如果date1=date2，则返回一个整数0；

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.

Examples：

The following example calculates the months between two dates:

SELECT MONTHS_BETWEEN
       (TO_DATE('02-02-1995','MM-DD-YYYY'),
        TO_DATE('01-01-1995','MM-DD-YYYY') ) "Months"
  FROM DUAL;

    Months
----------
1.03225806

 详见：https://docs.oracle.com/cd/E11882_01/server.112/e41084/functions102.htm#SQLRF00669