I am playing around with MongoDB trying to figure out how to do a simple
SELECT province, COUNT(*) FROM contest GROUP BY province
But I can
This type of query worked for me:
db.events.aggregate({$group: {_id : "$date", number: { $sum : 1} }} )
See http://docs.mongodb.org/manual/tutorial/aggregation-with-user-preference-data/
I need some extra operation based on the result of aggregate function. Finally I've found some solution for aggregate function and the operation based on the result in MongoDB. I've a collection Request
with field request, source, status, requestDate
.
Single Field Group By & Count:
db.Request.aggregate([
{"$group" : {_id:"$source", count:{$sum:1}}}
])
Multiple Fields Group By & Count:
db.Request.aggregate([
{"$group" : {_id:{source:"$source",status:"$status"}, count:{$sum:1}}}
])
Multiple Fields Group By & Count with Sort using Field:
db.Request.aggregate([
{"$group" : {_id:{source:"$source",status:"$status"}, count:{$sum:1}}},
{$sort:{"_id.source":1}}
])
Multiple Fields Group By & Count with Sort using Count:
db.Request.aggregate([
{"$group" : {_id:{source:"$source",status:"$status"}, count:{$sum:1}}},
{$sort:{"count":-1}}
])
If you need multiple columns to group by, follow this model. Here I am conducting a count by status
and type
:
db.BusinessProcess.aggregate({
"$group": {
_id: {
status: "$status",
type: "$type"
},
count: {
$sum: 1
}
}
})
Starting in MongoDB 3.4, you can use the $sortByCount
aggregation.
Groups incoming documents based on the value of a specified expression, then computes the count of documents in each distinct group.
https://docs.mongodb.com/manual/reference/operator/aggregation/sortByCount/
For example:
db.contest.aggregate([
{ $sortByCount: "$province" }
]);
Mongo shell command that worked for me:
db.getCollection(<collection_name>).aggregate([{"$match": {'<key>': '<value to match>'}}, {"$group": {'_id': {'<group_by_attribute>': "$group_by_attribute"}}}])
This would be the easier way to do it using aggregate:
db.contest.aggregate([
{"$group" : {_id:"$province", count:{$sum:1}}}
])