错误案例 Duplicate _id Values 如果_id 值不是全局唯一的,则重新分片操作会失败,以避免损坏集合数据。重复的 _id 值也会阻止成功的数据段迁移。如果您的文档具有重复的 _id 值,请将每个文档中的数据复制到新文档中,然后删除重复的文档。 后退 优化分片键 来年 更改文档的分区密钥值 ...
db.students.find({"age":19}).explain();{"queryPlanner":{"plannerVersion":1,"namespace":"mldn.students","indexFilterSet":false,"parsedQuery":{"age":{"$eq":19}},"winningPlan":{"stage":"FETCH","inputStage":{"stage":"IXSCAN","keyPattern":{"age":-1},"indexName":"age_-1","i...
sparse and unique Properties An index that is both sparse and unique prevents collection from having documents with duplicate values for a field but allows multiple documents that omit the key.例子 在A集合上创建稀疏索引 Consider a collection scores that contains the following documents: { "_id" ...
说明: 若插入的数据主键已经存在,则会抛 org.springframework.dao.DuplicateKeyException 异常,提示主键重复,不保存当前数据。 案例: 如向集合user_demo中插入一条数据: db.user_demo.insert({"name":"zhangsan","age":18})# 相当于sql中的insert into user_demo(name, age) values("zhangsan",18); 1.2 使...
//com.mongodb.MongoException$DuplicateKey: E11000 duplicate key error index: sample.user.$age_name_index dup key collection.ensureIndex(new BasicDBObject("age", -1).append("username", 1), "age_name_index", true); //根据索引名称删除 ...
insert(): 若插入的数据主键已经存在,则会抛 org.springframework.dao.DuplicateKeyException 异常,提示主键重复,不保存当前数据。 3.2 版本之后新增了 db.collection.insertOne() 和 db.collection.insertMany()。 db.collection.insertOne() 用于向集合插入一个新文档,语法格式如下: ...
When sorting on a field which contains duplicate values, documents containing those values may be returned in any order. If consistent sort order is desired, include at least one field in your sort that contains unique values. The easiest way to guarantee this is to include the _id field in...
mongodb unwind后 获取第一个 mongodb获取最大值,1.获取某个属性最大的value值并自增范例因为mongo不支持类似selectmax操作,也不支持递增int的操作,所以采用目前的方案table_name的记录,find输出时只输出type_id,按照type_id递减排序,取到第一个max_obj=stmt.find({"ta
insert(): 若插入的数据主键已经存在,则会抛org.springframework.dao.DuplicateKeyException异常,提示主键重复,不保存当前数据。 db.collectionName.insertOne(): 向指定集合中插入一条文档数据 db.collectionName.insertMany(): 向指定集合中插入多条文档数据 ...
To find the distinct values for a sharded collection, use the aggregation pipeline with the $group stage instead. For example: Instead of db.coll.distinct("x"), use db.coll.aggregate([ { $group: { _id: null, distinctValues: { $addToSet: "$x" } } }, { $project: { _id: 0 } ...