Insert six data:
The query has duplicate data:
Query and iterate delete duplicate data: Delete statement resolution: Db.userInfo.aggregate ([{$group: {_id: {userName: ' $userName ',Age : ' $age '},Count: {$sum: 1},dups: {$addToSet: ' $_id '}}}, {$match: {Count: {$GT: 1}}}]). ForEach (function (doc) {doc.dups.shift (); Db.userInfo.remove ({_id: {$in: Doc.dups}});}) 1. Based on the username and age groupings and statistics, $group returns only the fields participating in the grouping, using $addtoset to add _id field 2 to the returned result array. Use $match to match data 3 with a quantity greater than 1.doc.dups.shift (); means to delete from the first value of the array; The function is to kick apart one of the _id, so that the subsequent DELETE statement does not delete all the data4. Using the Foreach loop to delete data based on _id $addToSet operator adds a value to the array only if the value does not exist in the array. If the value already exists in the array, $addToSet returns and does not modify the array. Reference Address: http://forum.foxera.com/mongodb/topic/967/mongodb%E5%A6%82%E4%BD%95%E5%B0%86%E9%87%8D%E5%A4%8D%E7%9A%84% E6%95%b0%e6%8d%ae%e5%88%a0%e9%99%a4
MongoDB Delete duplicate data
