db={"students":[{"_id":"s1","name":"student1","age":10,"email":"student1@example.com"}],"teachers":[{"_id":"t1","name":"teacher1","age":20,"email":"teacher1@example.com"}],"stuffs":[{"_id":"st1","name":"stuffs","age":30,"email":"stuffs@example.com"}],"managers":[{"_id":"m1","name":"manager1","age":40,"email":"manager1@example.com"}]}

db.students.aggregate([{$match:{age:{$gte:25}}},{"$unionWith":{"coll":"teachers","pipeline":[{$match:{age:{$gte:25}}}]}},{"$unionWith":{"coll":"stuffs","pipeline":[{$match:{age:{$gte:25}}}]}},{"$unionWith":{"coll":"managers","pipeline":[{$match:{age:{$gte:25}}}]}}])