Count distinct value in MongoDB?

Use the concept of length to count distinct value. Following is the syntax −

db.yourCollectionName.distinct("yourFieldName").length;

Let us create a collection with documents −

> db.countDistinctDemo.insertOne({"StudentName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6166de8cc557214c0dfa") } > db.countDistinctDemo.insertOne({"StudentName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd616ade8cc557214c0dfb") } > db.countDistinctDemo.insertOne({"StudentName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd616cde8cc557214c0dfc") } > db.countDistinctDemo.insertOne({"StudentName":"Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6170de8cc557214c0dfd") } > db.countDistinctDemo.insertOne({"StudentName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6175de8cc557214c0dfe") } > db.countDistinctDemo.insertOne({"StudentName":"Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6181de8cc557214c0dff") }

Display all documents from a collection with the help of find() method −

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

This will produce the following output −

{ "_id" : ObjectId("5cbd6166de8cc557214c0dfa"), "StudentName" : "John" } { "_id" : ObjectId("5cbd616ade8cc557214c0dfb"), "StudentName" : "Chris" } { "_id" : ObjectId("5cbd616cde8cc557214c0dfc"), "StudentName" : "Chris" } { "_id" : ObjectId("5cbd6170de8cc557214c0dfd"), "StudentName" : "Carol" } { "_id" : ObjectId("5cbd6175de8cc557214c0dfe"), "StudentName" : "David" } { "_id" : ObjectId("5cbd6181de8cc557214c0dff"), "StudentName" : "Carol" }

Following is the query to count distinct value −

> db.countDistinctDemo.distinct("StudentName").length;

This will produce the following output −

4