presto-main/src/main/java/io/prestosql/sql/planner/optimizations/StreamPreferredProperties.java/StreamPreferredProperties/exactlyPartitionedOn
class StreamPreferredProperties:    public static StreamPreferredProperties exactlyPartitionedOn(Collection<Symbol> partitionSymbols)
    {
        if (partitionSymbols.isEmpty()) {
            return singleStream();
        }

        // this must be the exact partitioning symbols, in the exact order
        return new StreamPreferredProperties(Optional.of(FIXED), true, Optional.of(ImmutableList.copyOf(partitionSymbols)), false);
    }