@Override
  protected Optional<PlanNode> pushDownProjectOff(
      Context context, TableScanNode node, Set<Symbol> referencedOutputs) {
    return pruneColumns(node, referencedOutputs);
  }
This is a special case of PushProjectionIntoTableScan that performs only column pruning.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/iterative/rule/PruneTableScanColumns.java