@Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    FieldId fieldId = (FieldId) o;
    return fieldIndex == fieldId.fieldIndex && Objects.equals(relationId, fieldId.relationId);
  }
Returns {@link RelationType#indexOf(Field) field index} of the field in the containing
relation.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/FieldId.java