@Override
  public Object getRecordKey(KV record) {
    return record.getKey();
  }
This class joins incoming {@link SamzaSqlRelMessage} with records {@link KV} from a remote table with the join key
defined by the format of the table key.
samza-sql/src/main/java/org/apache/samza/sql/translator/SamzaSqlRemoteTableJoinFunction.java