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MongoDB query for counting the distinct values across all documents?
For this, use aggregate() in MongoDB. Let us create a collection with documents −
> db.demo718.insertOne(
... {
... "id":101,
... "details":
... {
... "OtherDetails": ["Chris", "Mike", "Sam"], "GroupName": ["Group-1"], "Info": []
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eaae25843417811278f5880")
}
> db.demo718.insertOne(
... {
... "id":102,
... "details":
... {
... "OtherDetails": ["Chris", "David"], "GroupName": ["Group-1"], "Info": []
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eaae25943417811278f5881")
}Display all documents from a collection with the help of find() method −
> db.demo718.find();
This will produce the following output −
{ "_id" : ObjectId("5eaae25843417811278f5880"), "id" : 101, "details" : { "OtherDetails" : [ "Chris", "Mike", "Sam" ], "GroupName" : [ "Group-1" ], "Info" : [ ] } }
{ "_id" : ObjectId("5eaae25943417811278f5881"), "id" : 102, "details" : { "OtherDetails" : [ "Chris", "David" ], "GroupName" : [ "Group-1" ], "Info" : [ ] } }Following is the query to count the distinct values across all documents −
> db.demo718.aggregate([
... {
... $unwind: "$details.GroupName"
... },
... {
... $match: {
... "details.GroupName": "Group-1"
... }
... },
... {
... $unwind: "$details.OtherDetails"
... },
... {
... $group: {
... _id: "$details.GroupName",
... OtherDetailsUnique: {
... $addToSet: "$details.OtherDetails"
... }
... }
... },
... {
... $project: {
... _id : 0,
... GROUP_NAME: "$_id",
... OtherDetailsUniqueCount: {
... $size: "$OtherDetailsUnique"
... }
... }
... }
... ])This will produce the following output −
{ "GROUP_NAME" : "Group-1", "OtherDetailsUniqueCount" : 4 }
Updated on: 14-May-2020
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