default int getPartialResultSize() {
    return 1;
  }
The return value equals to the length of tsBlockBuilder in {@link
#outputIntermediate(ColumnBuilder[])}}. Currently only aggregation `Avg, FirstValue, LastValue,
TimeDuration` will return 2.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/aggregation/Accumulator.java