private void appendOneRow(long currentTime) {
    for (int i = 0; i < outputColumnCount; i++) {
      ColumnMerger merger = mergers.get(i);
      merger.mergeColumn(
          inputTsBlocks,
          inputIndex,
          shadowInputIndex,
          currentTime,
          tsBlockBuilder.getColumnBuilder(i));
    }
  }
This field indicates each data type for output columns(not including time column) of
TimeJoinOperator its size should be equal to outputColumnCount.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/FullOuterTimeJoinOperator.java