public String toString() {
    return String.format("AggregationNode-%s", getPlanNodeId());
  }
If aggregation function COUNT and AVG for one time series appears at the same time, and outputs
intermediate result, the output columns will be like | COUNT | COUNT | SUM |. In this
situation, one COUNT column is not needed. Therefore, when COUNT(or SUM) appears with AVG and
outputs intermediate result(if they output final result, they will be all necessary), we need
to REMOVE the COUNT aggregation, and only keep AVG function no matter their appearing order.

<p>The related functions include AVG(COUNT AND SUM), FIRST_VALUE(FIRST_VALUE AND MIN_TIME),
LAST_VALUE(LAST_VALUE AND MAX_TIME).
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/node/process/AggregationNode.java