How to select where sum of fields is greater than a value in MongoDB?

You can use $where operator for this. Let us first create a collection with documents −

> db.sumOfFieldIsGreaterThanDemo.insertOne({"Price1":10,"Price2":50,"Price3":40});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cdd84b8bf3115999ed511e6")
}
> db.sumOfFieldIsGreaterThanDemo.insertOne({"Price1":11,"Price2":1,"Price3":120});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cdd84c6bf3115999ed511e7")
}
> db.sumOfFieldIsGreaterThanDemo.insertOne({"Price1":10,"Price2":9,"Price3":6});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cdd84d2bf3115999ed511e8")
}

Following is the query to display all documents from a collection with the help of find() method −

> db.sumOfFieldIsGreaterThanDemo.find();

This will produce the following output −

{ "_id" : ObjectId("5cdd84b8bf3115999ed511e6"), "Price1" : 10, "Price2" : 50, "Price3" : 40 }
{ "_id" : ObjectId("5cdd84c6bf3115999ed511e7"), "Price1" : 11, "Price2" : 1, "Price3" : 120 }
{ "_id" : ObjectId("5cdd84d2bf3115999ed511e8"), "Price1" : 10, "Price2" : 9, "Price3" : 6 }

Following is the query to select where sum of fields is greater than a value in MongoDB −

> db.sumOfFieldIsGreaterThanDemo.find(
   {$where: function() {
      return this.Price1+this.Price2+this.Price3 > 100
   }}
);

This will produce the following output −

{ "_id" : ObjectId("5cdd84c6bf3115999ed511e7"), "Price1" : 11, "Price2" : 1, "Price3" : 120 }