[{"_id":1,"auto-generated-number":23,"section-1":1},{"_id":2,"auto-generated-number":23,"section-1":1},{"_id":3,"auto-generated-number":24,"section-1":1},{"_id":4,"auto-generated-number":23,"section-1":2},]

db.collection.aggregate([{$group:{_id:{"section-1":"$section-1","auto-generated-number":"$auto-generated-number"},count:{$sum:1}}},{$match:{count:{$gt:1}}}])