@SuppressWarnings("unchecked")
    public static <T extends Number & Comparable> WindowOver<T> ntile(T num) {
        return new WindowOver<T>((Class<T>) num.getClass(), SQLOps.NTILE, ConstantImpl.create(num));
    }
divides an ordered data set into a number of buckets indicated by expr and assigns the
appropriate bucket number to each row

@param num bucket size
@return ntile(num)
querydsl-sql/src/main/java/com/querydsl/sql/SQLExpressions.java