public static UnsafeExternalRowSorter.PrefixComputer createPrefixGenerator(List<DataType> schema) {
        if (schema.size() != 0) {
            return row -> row.getUniformVal(0);
        } else {
            return row -> 0;
        }
    }
Creates the prefix computer for the first field in the given schema, in ascending order.
indexr-query-opt/src/main/java/io/indexr/query/util/SortPrefixUtils.java