code: public static <T extends Number> WithinGroup<T> percentileDisc(Expression<T> arg) {
          return new WithinGroup<T>(arg.getType(), SQLOps.PERCENTILEDISC, arg);
      }
docs: PERCENTILE_DISC is an inverse distribution function that assumes a discrete distribution model.
  It takes a percentile value and a sort specification and returns an element from the set.
  Nulls are ignored in the calculation.
  
  <p>This function takes as an argument any numeric datatype or any nonnumeric datatype that can be
  implicitly converted to a numeric datatype. The function returns the same datatype as the numeric
  datatype of the argument.</p>
  
  @param arg argument
  @return percentile_disc(arg)