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