Find duplicate records in MongoDB [duplicate]

问题:

This question already has an answer here:

• MongoDB Duplicate Documents even after adding unique key 2 answers

How would I find duplicate fields in a mongo collection.

I'd like to check if any of the "name" fields are duplicates.

{
    "name" : "ksqn291",
    "__v" : 0,
    "_id" : ObjectId("540f346c3e7fc1054ffa7086"),
    "channel" : "Sales"
}

Many thanks!

回答1:

Use aggregation on name and get name with count > 1:

db.collection.aggregate(
    {"$group" : { "_id": "$name", "count": { "$sum": 1 } } },
    {"$match": {"_id" :{ "$ne" : null } , "count" : {"$gt": 1} } }, 
    {"$project": {"name" : "$_id", "_id" : 0} }
)

To sort the results by most to least duplicates:

db.collection.aggregate(
    {"$group" : { "_id": "$name", "count": { "$sum": 1 } } },
    {"$match": {"_id" :{ "$ne" : null } , "count" : {"$gt": 1} } }, 
    {"$sort": {"count" : -1} },
    {"$project": {"name" : "$_id", "_id" : 0} }     
)

To use with another column name than "name", change "$name" to "$column_name"

回答2:

You can find the list of duplicate names using the following aggregate pipeline:

• Group all the records having similar name.
• Match those groups having records greater than 1.
• Then group again to project all the duplicate names as an array.

The Code:

db.collection.aggregate([
{$group:{"_id":"$name","name":{$first:"$name"},"count":{$sum:1}}},
{$match:{"count":{$gt:1}}},
{$project:{"name":1,"_id":0}},
{$group:{"_id":null,"duplicateNames":{$push:"$name"}}},
{$project:{"_id":0,"duplicateNames":1}}
])

o/p:

{ "duplicateNames" : [ "ksqn291", "ksqn29123213Test" ] }

回答3:

The answer anhic gave can be very inefficient if you have a large database and the attribute name is present only in some of the documents.

To improve efficiency you can add a $match to the aggregation.

db.collection.aggregate(
    {"$match": {"name" :{ "$ne" : null } } }, 
    {"$group" : {"_id": "$name", "count": { "$sum": 1 } } },
    {"$match": {"count" : {"$gt": 1} } }, 
    {"$project": {"name" : "$_id", "_id" : 0} }
)

回答4:

db.collectionName.aggregate([
{ $group:{
    _id:{Name:"$name"},
    uniqueId:{$addToSet:"$_id"},
    count:{"$sum":1}
  } 
},
{ $match:{
  duplicate:{"$gt":1}
 }
}
]);

First Group Query the group according to the fields.

Then we check the unique Id and count it, If count is greater then 1 then the field is duplicate in the entire collection so that thing is to be handle by $match query.