class_docstr: This plan is used for pushing down query string directly to
  backend database engine.
code: def query_string(self):
      return self._query_string
  
file_path: evadb/evadb/plan_nodes/native_plan.py
imports: from evadb.plan_nodes.abstract_plan import AbstractPlan
  from evadb.plan_nodes.types import PlanOprType
label_desc: Use image node_id 3 for calling the NativePlan obj's underlying member method code with example usage: obj.query_string() and returns: self