public Collection<Field> getAllFields() {
    return ImmutableSet.copyOf(allFields);
  }
Gets all fields including hidden fields. No assumptions should be made about the order of the
fields returned from this method. To obtain the index of a field, call indexOf.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/RelationType.java