protected void appendLeftWithEmptyRight() {
    while (leftIndex < leftBlock.getPositionCount()) {
      appendLeftBlockData(leftOutputSymbolIdx, resultBuilder, leftBlock, leftIndex);

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

      resultBuilder.declarePosition();
      leftIndex++;
    }
  }
@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