class_docstr: This plan is used for storing information required for union operations.
  
  Arguments:
      all: Bool
          UNION (deduplication) vs UNION ALL (non-deduplication)
code: def __str__(self):
      return "UnionAllPlan" if self._all else "UnionPlan"
  
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 UnionPlan obj's underlying member method code with example usage: obj.__str__() and returns: unknown