support function months_between/add_months

[HackervvSKvasdlK]

Feature Request

Is your feature request related to a problem? Please describe:

Describe the feature you'd like:
add_months/months_between:
We now have calculation requirements for month addition and subtraction and monthly difference, and the result needs to be consistent with Oracle/Hive. May I ask whether these two functions can be implemented. Example:
add_months('2019-2-28',1)=2019-3-31
add_months('2020-2-28',1)=2019-3-28
add_months('2020-2-29',1)=2019-3-31
add_months('2020-2-28',-1)=2019-1-28
add_months('2020-2-29',-1)=2019-1-31
add_months('2020-3-31',-1)=2020-2-29
add_months('2020-3-30',-1)=2020-2-29
add_months('2020-3-29',-1)=2020-2-29
add_months('2019-2-28',-1)=2019-1-31
add_months('2019-3-31',-1)=2019-2-28

The implementation in Hive is:
months_between:
public Object evaluate(DeferredObject[] arguments) throws HiveException {
// the function should support both short date and full timestamp format
// time part of the timestamp should not be skipped
Date date1 = getTimestampValue(arguments, 0, tsConverters);
if (date1 == null) {
date1 = getDateValue(arguments, 0, dtInputTypes, dtConverters);
if (date1 == null) {
return null;
}
}

Date date2 = getTimestampValue(arguments, 1, tsConverters);
if (date2 == null) {
  date2 = getDateValue(arguments, 1, dtInputTypes, dtConverters);
  if (date2 == null) {
    return null;
  }
}

cal1.setTime(date1);
cal2.setTime(date2);

// skip day/time part if both dates are end of the month
// or the same day of the month
int monDiffInt = (cal1.get(YEAR) - cal2.get(YEAR)) * 12 + (cal1.get(MONTH) - cal2.get(MONTH));
if (cal1.get(DATE) == cal2.get(DATE)
    || (cal1.get(DATE) == cal1.getActualMaximum(DATE) && cal2.get(DATE) == cal2
        .getActualMaximum(DATE))) {
  output.set(monDiffInt);
  return output;
}

int sec1 = getDayPartInSec(cal1);
int sec2 = getDayPartInSec(cal2);

// 1 sec is 0.000000373 months (1/2678400). 1 month is 31 days.
// there should be no adjustments for leap seconds
double monBtwDbl = monDiffInt + (sec1 - sec2) / 2678400D;
// Round a double to 8 decimal places.
double result = BigDecimal.valueOf(monBtwDbl).setScale(8, ROUND_HALF_UP).doubleValue();
output.set(result);
return output;

}

add_months:
protected Calendar addMonth(Date d, int numMonths) {
calendar.setTime(d);

boolean lastDatOfMonth = isLastDayOfMonth(calendar);

calendar.add(Calendar.MONTH, numMonths);

if (lastDatOfMonth) {
  int maxDd = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
  calendar.set(Calendar.DAY_OF_MONTH, maxDd);
}
return calendar;

}