Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"id":1},{"id":2},{"id":1},{"id":3},{"id":4}]
Query
db.collection.aggregate([{$group:{_id:null,ids:{$addToSet:"$id"}}},{$project:{_id:"$ids"}}])
Result