presto-main/src/main/java/io/prestosql/operator/RowNumberOperator.java/RowNumberOperator/toTypes
class RowNumberOperator:    private static List<Type> toTypes(List<? extends Type> sourceTypes, List<Integer> outputChannels)
    {
        ImmutableList.Builder<Type> types = ImmutableList.builder();
        for (int channel : outputChannels) {
            types.add(sourceTypes.get(channel));
        }
        types.add(BIGINT);
        return types.build();
    }