@Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    RelationId that = (RelationId) o;
    return sourceNode.isPresent()
        && that.sourceNode.isPresent()
        && sourceNode.equals(that.sourceNode);
  }
Creates {@link RelationId} equal only to itself
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/RelationId.java