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 all(self):
      return self._all
  
imports: from evadb.plan_nodes.abstract_plan import AbstractPlan
  from evadb.plan_nodes.types import PlanOprType
label_desc: Use image node_id 2 for calling the UnionPlan obj's underlying member method code with example usage: obj.all() and returns: self