Match between fields in MongoDB aggregation framework?

      You can use $cmp operator for this. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.matchBetweenFieldsDemo.insertOne({"FirstValue":40,"SecondValue":70});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c92c9625259fcd19549980d")
}
> db.matchBetweenFieldsDemo.insertOne({"FirstValue":20,"SecondValue":5});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c92c96b5259fcd19549980e")
}

Display all documents from a collection with the help of find() method. The query is as follows −

> db.matchBetweenFieldsDemo.find().pretty();

The following is the output −

{
   "_id" : ObjectId("5c92c9625259fcd19549980d"),
   "FirstValue" : 40,
   "SecondValue" : 70
}
{
   "_id" : ObjectId("5c92c96b5259fcd19549980e"),
   "FirstValue" : 20,
"SecondValue" : 5
}

Here is the query to $match between fields in aggregation framework −

> db.matchBetweenFieldsDemo.aggregate([
   ... {$project: {
      ...
      ... firstGreaterThanOrNot: {$cmp: ['$FirstValue', '$SecondValue']}
   ... }},
   ... {$match: {firstGreaterThanOrNot:{$gt: 0}}}
... ]);

The following is the output −

{ "_id" : ObjectId("5c92c96b5259fcd19549980e"), "firstGreaterThanOrNot" : 1 }