Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{node:"a",value:"3"},{node:"c",value:"3"},{node:"a",value:"1"},{node:"a",value:"4"}]
Query
db.collection.aggregate([{$match:{node:{$in:["a","b","c"]}}},{$group:{"_id":"$node"}}])
Result