protected void resetLeftBlock() {
    leftBlock = null;
    leftIndex = 0;
  }
This method will be invoked when any left data matches right data on the join criteria. Only
outer join will use this method currently, outer join may record the last matched rows to avoid
append results which is already output.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/AbstractMergeSortJoinOperator.java