odb索引

MongoDB 索引

语法 createIndex()方法基本语法格式如下所示：>db.collection.createIndex(keys,options)语法中 Key 值为你要创建的索引字段，1 为指定按升序创建索引，如果你想按降序来创建索引指定为-1 即可。实例>db.col.createIndex({"title":1})>...

MySQL innodb 索引

1.系统版本说明 mysql 5.7.25，...5.索引下推 MySQL新引入的功能，若在使用联合索引过程中，根据最左前缀的原则命中了联合索引后，若WHERE语句的下一个字段也在联合索引中，则对之前联合索引所命中的主键值进行进一步过滤，以减少回表操作。

MongoDB 索引创建

db.products.createIndex({ item:1,quantity:1 })比如上面的索引创建后，其索引名为item_1_quantity_-1 可以指定自定义的索引名称 db.products.createIndex({ item:1,quantity:1 },{ name:"inventory_idx"})如上方式，我们指定了了索引名称...

MongoDB索引原理

不光能满足多个字段组合起来的查询，比如db.person.find({age：18，name:"jack"})，也能满足所以能匹配符合索引前缀的查询，这里{age:1}即为{age:1,name:1}的前缀，所以类似db.person.find({age：18})的查询也能通过该索引来加速；...

MongoDB索引管理——创建索引，查看索引，删除索引，重建索引

age":25,"gender":"F"} {"name":"zhangsan","age":25,"gender":"F"}>db.users.insert(user1)WriteResult({"nInserted":1 })>db.users.count()2 创建索引：mongodb使用createIndex()和ensureIndex()方法来创建索引，前者用于3.0及以上版本...

MongoDB索引介绍

一、Single Field Indexes 示例文档：{"_id":ObjectId("570c04a4ad233577f97dc459"),"score":1034,"location":{ state:"NY",city:"New York"} } 1、语法：db.records.createIndex({ score:1 })2、在嵌套字段上创建索引 db.records....

MongoDB索引使用

提升数据库检索性能的手段通过getIndexes()来获取已经存在的索引内容 db.students.getIndexes();1*/[{"v":1,"key":{"_id":1 },"name":"_id_","ns":"mldn.students"}]创建自己的索引范例：创建一个索引，在age列加一个将序索引 db....

mysql innodb索引原理

联合索引中如果查询中有某个列的范围查询，则其右边的所有列都无法使用索查询优化器不一定会使用索引在执行SQL时，查询优化器会判断使用索引的效率问题，如果优化器认为使用索引还不如全表扫描高效，那么就会弃用索引而使用全表扫描。...

MongoDB索引属性介绍

一、TTL索引 1、语法 db.eventlog.createIndex({"lastModifiedDate":1 },{ expireAfterSeconds:3600 })2、TTL索引的功效 TTL索引会根据TTL索引字段在一定的时间限制后自动删除过期文档，TTL索引更多的适用于只需要保存有限时间的集合，如...

MongoDB·引擎特性·MongoDB索引原理

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云数据库 HBase 版

云数据库HBase是面向大数据领域的一站式NoSQL服务，100%兼容开源HBase并深度扩展，支持海量数据下的实时存储、高并发吞吐、轻SQL分析等，是风控、推荐、广告、物联网、车联网、Feeds流、数据大屏等场景首选数据库。

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