@Override
  public Pattern<TableFunctionProcessorNode> getPattern() {
    return PATTERN;
  }
This rule prunes unreferenced outputs of TableFunctionProcessorNode. Any source output symbols
not included in the required symbols can be pruned.

<p>First, it extracts all symbols required for:

<ul>
  <li>- pass-through
  <li>- table function computation
  <li>- partitioning and ordering (including the hashSymbol)
</ul>

<p>Next, a mapping of input symbols to marker symbols is updated so that it only contains
mappings for the required symbols.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/iterative/rule/PruneTableFunctionProcessorSourceColumns.java