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Group across two columns in MongoDB?
To group across two columns, use $lookup. Let us create a collection with documents −
> db.demo132.insertOne({"CountryName1":"US","CountryName2":"UK",Value:50});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e31950468e7f832db1a7f75")
}
> db.demo132.insertOne({"CountryName1":"UK","CountryName2":"AUS",Value:10});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e31951d68e7f832db1a7f76")
}
> db.demo132.insertOne({"CountryName1":"AUS","CountryName2":"US",Value:40});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e31952c68e7f832db1a7f77")
}Display all documents from a collection with the help of find() method −
> db.demo132.find();
This will produce the following output −
{ "_id" : ObjectId("5e31950468e7f832db1a7f75"), "CountryName1" : "US", "CountryName2" : "UK", "Value" : 50 }
{ "_id" : ObjectId("5e31951d68e7f832db1a7f76"), "CountryName1" : "UK", "CountryName2" : "AUS", "Value" : 10 }
{ "_id" : ObjectId("5e31952c68e7f832db1a7f77"), "CountryName1" : "AUS", "CountryName2" : "US", "Value" : 40 }Following is the query to group across two columns in MongoDB −
> db.demo132.aggregate( [
... {
... "$lookup" : {
... "from" : "demo132",
... "localField" : "CountryName1",
... "foreignField" : "CountryName2",
... "as" : "out"
... }
... },
... {
... "$unwind" : "$out"
... },
... {
... "$project" : {
... "_id" : 0,
... "CountryName1" : 1,
... "total" : { "$sum" : [ "$Value", "$out.Value"]}
... }
... }
... ])This will produce the following output −
{ "CountryName1" : "US", "total" : 90 }
{ "CountryName1" : "UK", "total" : 60 }
{ "CountryName1" : "AUS", "total" : 50 }
Updated on: 31-Mar-2020
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