mongodb - How to query the maximum value of updateAt in each userId

Question

{
    userId: OjbectId,
    updatedAt: Date
}

I am a newbie, please give me some advice.

Answer 1

If you know how to write it in SQL, the same principle applies to MongoDB. This is a very common grouped aggregation query. The answers are below, but I still hope you can try to search for the answers online and exercise your ability to solve problems independently.

db.collection.aggregate([
  {$group: {_id: "$userId", maxUpdatedAt: {$max: "$updatedAt"}}}
]);

The answer can be easily obtained using aggregation’s $max operator.