presto-main/src/main/java/io/prestosql/sql/planner/plan/SemiJoinNode.java/SemiJoinNode/getOutputSymbols
class SemiJoinNode:    @Override
    public List<Symbol> getOutputSymbols()
    {
        return ImmutableList.<Symbol>builder()
                .addAll(source.getOutputSymbols())
                .add(semiJoinOutput)
                .build();
    }