code: public CassandraJavaRDD<R> select(ColumnRef... columns) {
          Seq<ColumnRef> columnRefs = JavaApiHelper.toScalaSeq(columns);
          CassandraRDD<R> newRDD = rdd().select(columnRefs);
          return wrap(newRDD);
      }
docs: Narrows down the selected set of columns.
  <p/>
  Use this for better performance, when you don't need all the columns in the result RDD. When
  called multiple times, it selects the subset of the already selected columns, so after a column
  was removed by the previous {@code select} call, it is not possible to add it back.</p>