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How to select documents with values above the average in MongoDB?
Use aggregate() in MongoDB to select documents with values above the average. To find the average, use $avg in MongoDB.
Let us create a collection with documents −
> db.demo552.insertOne({values:10});{
"acknowledged" : true, "insertedId" : ObjectId("5e8e3b1c9e5f92834d7f05ea")
}
> db.demo552.insertOne({values:50});{
"acknowledged" : true, "insertedId" : ObjectId("5e8e3b1f9e5f92834d7f05eb")
}
> db.demo552.insertOne({values:40});{
"acknowledged" : true, "insertedId" : ObjectId("5e8e3b289e5f92834d7f05ec")
}Display all documents from a collection with the help of find() method −
> db.demo552.find();
This will produce the following output −
{ "_id" : ObjectId("5e8e3b1c9e5f92834d7f05ea"), "values" : 10 }
{ "_id" : ObjectId("5e8e3b1f9e5f92834d7f05eb"), "values" : 50 }
{ "_id" : ObjectId("5e8e3b289e5f92834d7f05ec"), "values" : 40 }Following is the query to select documents with values above the average −
> var findAvg = db.demo552.aggregate([
... { "$group": { "_id": "null", Average: { "$avg": "$values"} }}
... ]).toArray()[0]["Average"];
> db.demo552.find({ "values": { "$gt": findAvg } })This will produce the following output −
{ "_id" : ObjectId("5e8e3b1f9e5f92834d7f05eb"), "values" : 50 }
{ "_id" : ObjectId("5e8e3b289e5f92834d7f05ec"), "values" : 40 }
Updated on: 14-May-2020
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