@Override
  public int isNullable(int column) throws SQLException {
    RequestDelegate<Integer> delegate = createRequestDelegate();
    for (ResultSetMetaData rs : metaDataList) {
      delegate.addRequest(() -> rs.isNullable(column));
    }
    return delegate.requestAllAndCompare();
  }
The implementation of {@link ResultSetMetaData} in cluster test.
integration-test/src/main/java/org/apache/iotdb/itbase/runtime/ClusterResultSetMetaData.java