protected void appendOneLeftRowWithEmptyRight() {
    appendLeftBlockData(leftOutputSymbolIdx, resultBuilder, leftBlock, leftIndex);

    for (int i = 0; i < rightOutputSymbolIdx.length; i++) {
      ColumnBuilder columnBuilder = resultBuilder.getColumnBuilder(leftOutputSymbolIdx.length + i);
      columnBuilder.appendNull();
    }

    resultBuilder.declarePosition();
  }
@return true if current right block is consumed up
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/AbstractMergeSortJoinOperator.java