@Override
  public List<Symbol> getOutputSymbols() {
    return ImmutableList.<Symbol>builder()
        .addAll(leftOutputSymbols)
        .addAll(rightOutputSymbols)
        .build();
  }
@return a new JoinNode with the flipped attributes
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/node/JoinNode.java