public RelationType joinWith(RelationType other) {
    List<Field> fields =
        ImmutableList.<Field>builder().addAll(this.allFields).addAll(other.allFields).build();

    return new RelationType(fields);
  }
Creates a new tuple descriptor containing all fields from this tuple descriptor and all fields
from the specified tuple descriptor.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/RelationType.java