class_docstr: Merge the seq scan queries
  Arguments:
      node (AbstractPlan): The UnionPlan
code: def exec(self, *args, **kwargs) -> Iterator[Batch]:
      assert self.node.all is True, "Only UNION ALL is supported now."
  
      # We should have only two children
      for child in self.children:
          for batch in child.exec():
              yield batch
  
file_path: evadb/evadb/executor/union_executor.py
imports: from typing import Iterator
  from evadb.database import EvaDBDatabase
  from evadb.executor.abstract_executor import AbstractExecutor
  from evadb.models.storage.batch import Batch
  from evadb.plan_nodes.union_plan import UnionPlan
label_desc: Use image node_id 2 for calling the UnionExecutor obj's underlying member method code with example usage: obj.exec() without return types