code: public static <D extends Comparable> NumberExpression<Integer> datediff(DatePart unit,
              DateExpression<D> start, DateExpression<D> end) {
          return Expressions.numberOperation(Integer.class, DATE_DIFF_OPS.get(unit), start, end);
      }
docs: Get a datediff(unit, start, end) expression
  
  @param unit date part
  @param start start
  @param end end
  @return difference in units