protected void appendLeftBlockData(
      int[] leftOutputSymbolIdx, TsBlockBuilder resultBuilder, TsBlock leftBlock, int leftIndex) {
    for (int i = 0; i < leftOutputSymbolIdx.length; i++) {
      int idx = leftOutputSymbolIdx[i];
      ColumnBuilder columnBuilder = resultBuilder.getColumnBuilder(i);
      if (leftBlock.getColumn(idx).isNull(leftIndex)) {
        columnBuilder.appendNull();
      } else {
        columnBuilder.write(leftBlock.getColumn(idx), 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