MongoDB query to gather unique array item?

To gather a unique array items, use distinct(). Let us create a collection with documents −

> db.demo588.insertOne({"CountryName":["US","AUS","UK","US","UK","AUS"]});{
   "acknowledged" : true, "insertedId" : ObjectId("5e92bbd2fd2d90c177b5bccb")
}

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

> db.demo588.find().pretty();

This will produce the following output −

{
   "_id" : ObjectId("5e92bbd2fd2d90c177b5bccb"),
   "CountryName" : [
      "US",
      "AUS",
      "UK",
      "US",
      "UK",
      "AUS"
   ]
}

Following is the query to gather unique array item −

> db.demo588.distinct("CountryName");

This will produce the following output −

[ "AUS", "UK", "US" ]