MongoDB学习（二）索引的用法

MongoDB与sql关于库表的名字：

database == database

collection == table

document == row

本篇转载自：http://blog.nosqlfan.com/html/271.html

索引能提高检索数据的速度，你可以想像成在MySQL中创建索引一样，同样索引也是用B-Tree也实现的。

1.单列索引

在字段x上创建索引，1 (表示升序) or -1 (表示降序)

> db.data.ensureIndex({x:1})

显示表data里面的所有索引

> db.data.getIndexes()
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
}
]

查找字段x为6的值，此时已经用到索引了

> db.data.find({x:6})
{ "_id" : ObjectId("4bee804ba23d558eb6687117"), "x" : 6, "name" : "caihuafeng1" }
{ "_id" : ObjectId("4bee804ba23d558eb6687118"), "x" : 6, "name" : "caihuafeng2" }
{ "_id" : ObjectId("4bee804ba23d558eb6687119"), "x" : 6, "name" : "caihuafeng3" }
{ "_id" : ObjectId("4bee804ba23d558eb668711a"), "x" : 6, "name" : "caihuafeng4" }
{ "_id" : ObjectId("4bee804ba23d558eb668711b"), "x" : 6, "name" : "caihuafeng5" }
{ "_id" : ObjectId("4bee804ba23d558eb668711c"), "x" : 6, "name" : "caihuafeng6" }
{ "_id" : ObjectId("4bee804ba23d558eb668711d"), "x" : 6, "name" : "caihuafeng7" }
{ "_id" : ObjectId("4bee804ba23d558eb668711e"), "x" : 6, "name" : "caihuafeng8" }
{ "_id" : ObjectId("4bee804ba23d558eb668711f"), "x" : 6, "name" : "caihuafeng9" }
{ "_id" : ObjectId("4bee804ba23d558eb6687120"), "x" : 6, "name" : "caihuafeng10" }

2.默认索引
上述1中db.data.getIndexes()显示出来的一共有2个索引，其中_id是创建表的时候自动创建的索引，此索引是不能够删除的。

3.文档作为索引的键值
a.单列索引

往数据库recommender的表data中插入三条记录

> db.data.insert({name:"1616",info:{url:"http://www.1616.net/",city:"beijing"}});
> db.data.insert({name:"hao123",info:{url:"http://www.hao123.com/",city:"beijing"}});
> db.data.insert({name:"ll4la",info:{url:"http://www.114la.com/",city:"dongguan"}});

对字段info创建索引

> db.data.ensureIndex({info: 1});

显示表data上的所有索引

> db.data.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
},
{
"_id" : ObjectId("4befb76bb0e29ba1ce20e0bf"),
"ns" : "recommender.data",
"key" : {
"info" : 1
},
"name" : "info_1"
}
]

查找指定的记录，此时会用到索引

> db.data.find({info: {url:"http://www.1616.net/",city:"beijing"}});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }

b.组合索引
建立组合索引

> db.data.ensureIndex({"info.url":1, "info.city":1});
> db.data.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
},
{
"_id" : ObjectId("4befb76bb0e29ba1ce20e0bf"),
"ns" : "recommender.data",
"key" : {
"info" : 1
},
"name" : "info_1"
},
{
"_id" : ObjectId("4befb9d1b0e29ba1ce20e0c0"),
"ns" : "recommender.data",
"key" : {
"info.url" : 1,
"info.city" : 1
},
"name" : "info.url_1_info.city_1"
}
]

下面几个操作均会用到索引

> db.data.find({"info.url": "http://www.1616.net/", "info.city": "beijing"});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }

> db.data.find({"info.url": "http://www.1616.net/"});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }

1表示升序(asc)，-1表示降序(desc)

> db.data.find({"info.url": /http:*/i}).sort({"info.url": 1, "info.city": 1});
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }

> db.data.find({"info.url": /http:*/i}).sort({"info.url": 1});
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }

> db.data.find({"info.url": /http:*/i}).sort({"info.url": -1});
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }

4.组合索引
注意，这里的组合索引与上述3中的b中的组合索引是有点不同的，4里面是对一级字段建立组合索引，而上述3中是对二级字段建立组合索引。

在字段name及info上面创建组合索引

> db.data.ensureIndex({name: 1, info: -1});

MongoDB中索引的用法

作者：nosqlfan on 星期四, 六月 24, 2010 · 1条评论【阅读：2,024 次】

本文是一篇转载文章，作者在对MongoDB 文档进行了细致的阅读后，总结出了MongoDB的各种索引的用法。

原文链接：http://iamcaihuafeng.blog.sohu.com/151638529.html

索引能提高检索数据的速度，你可以想像成在MySQL中创建索引一样，同样索引也是用B-Tree也实现的。

1.单列索引
在字段x上创建索引，1 (ascending) or -1 (descending)

> db.data.ensureIndex({x:1})

显示表data里面的所有索引

> db.data.getIndexes()
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
}
]

查找字段x为6的值，此时已经用到索引了

> db.data.find({x:6})
{ "_id" : ObjectId("4bee804ba23d558eb6687117"), "x" : 6, "name" : "caihuafeng1" }
{ "_id" : ObjectId("4bee804ba23d558eb6687118"), "x" : 6, "name" : "caihuafeng2" }
{ "_id" : ObjectId("4bee804ba23d558eb6687119"), "x" : 6, "name" : "caihuafeng3" }
{ "_id" : ObjectId("4bee804ba23d558eb668711a"), "x" : 6, "name" : "caihuafeng4" }
{ "_id" : ObjectId("4bee804ba23d558eb668711b"), "x" : 6, "name" : "caihuafeng5" }
{ "_id" : ObjectId("4bee804ba23d558eb668711c"), "x" : 6, "name" : "caihuafeng6" }
{ "_id" : ObjectId("4bee804ba23d558eb668711d"), "x" : 6, "name" : "caihuafeng7" }
{ "_id" : ObjectId("4bee804ba23d558eb668711e"), "x" : 6, "name" : "caihuafeng8" }
{ "_id" : ObjectId("4bee804ba23d558eb668711f"), "x" : 6, "name" : "caihuafeng9" }
{ "_id" : ObjectId("4bee804ba23d558eb6687120"), "x" : 6, "name" : "caihuafeng10" }

2.默认索引
上述1中db.data.getIndexes()显示出来的一共有2个索引，其中_id是创建表的时候自动创建的索引，此索引是不能够删除的。

An index is always created on _id. This index is special and cannot be deleted. The _id index enforces uniqueness for its keys.

3.文档作为索引的键值
a.单列索引
MongoDB的官方文档上面是这样说的:
Documents as Keys

Indexed fields may be of any type, including documents:

往数据库recommender的表data中插入三条记录

> db.data.insert({name:"1616",info:{url:"http://www.1616.net/",city:"beijing"}});
> db.data.insert({name:"hao123",info:{url:"http://www.hao123.com/",city:"beijing"}});
> db.data.insert({name:"ll4la",info:{url:"http://www.114la.com/",city:"dongguan"}});

对字段info创建索引

> db.data.ensureIndex({info: 1});

显示表data上的所有索引

> db.data.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
},
{
"_id" : ObjectId("4befb76bb0e29ba1ce20e0bf"),
"ns" : "recommender.data",
"key" : {
"info" : 1
},
"name" : "info_1"
}
]

查找指定的记录，此时会用到索引

> db.data.find({info: {url:"http://www.1616.net/",city:"beijing"}});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }

b.组合索引
建立组合索引

> db.data.ensureIndex({"info.url":1, "info.city":1});
> db.data.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
},
{
"_id" : ObjectId("4befb76bb0e29ba1ce20e0bf"),
"ns" : "recommender.data",
"key" : {
"info" : 1
},
"name" : "info_1"
},
{
"_id" : ObjectId("4befb9d1b0e29ba1ce20e0c0"),
"ns" : "recommender.data",
"key" : {
"info.url" : 1,
"info.city" : 1
},
"name" : "info.url_1_info.city_1"
}
]

下面几个操作均会用到索引

> db.data.find({"info.url": "http://www.1616.net/", "info.city": "beijing"});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }

> db.data.find({"info.url": "http://www.1616.net/"});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }

1表示升序(asc)，-1表示降序(desc)

> db.data.find({"info.url": /http:*/i}).sort({"info.url": 1, "info.city": 1});
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }

> db.data.find({"info.url": /http:*/i}).sort({"info.url": 1});
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }

> db.data.find({"info.url": /http:*/i}).sort({"info.url": -1});
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114 la.com/", "city" : "dongguan" } }

在字段name及info上面创建组合索引

> db.data.ensureIndex({name: 1, info: -1});

显示所有的索引

> db.data.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.data",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befb146b0e29ba1ce20e0bb"),
"ns" : "recommender.data",
"key" : {
"x" : 1
},
"name" : "x_1"
},
{
"_id" : ObjectId("4befb76bb0e29ba1ce20e0bf"),
"ns" : "recommender.data",
"key" : {
"info" : 1
},
"name" : "info_1"
},
{
"_id" : ObjectId("4befb9d1b0e29ba1ce20e0c0"),
"ns" : "recommender.data",
"key" : {
"info.url" : 1,
"info.city" : 1
},
"name" : "info.url_1_info.city_1"
},
{
"_id" : ObjectId("4befbfcfb0e29ba1ce20e0c1"),
"ns" : "recommender.data",
"key" : {
"name" : 1,
"info" : -1
},
"name" : "name_1_info_-1"
}
]

下面的排序将用到上面的索引

> db.data.find({"info.url": /http:*/i}).sort({name:1, info: -1});
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }

5.唯一索引

往表data中插入一条记录。

> db.data.insert({firstname: "cai", lastname: "huafeng"});

由于表data中只有一记录有字段firstname及lastname，其它的行均没有相应的值，也就是均为null，为null就说明是相同的，而唯一索引是不允许有相同的值的，所以下面创建唯一组合索引时报错了。

所以建立唯一索引时，不管是对单个字段还是多个字段建立索引，则最好每一行均有此字段，否则会报错。

> db.data.find();
{ "_id" : ObjectId("4bee745a0863b1c233b8b7ea"), "name" : "caihuafeng" }
{ "_id" : ObjectId("4bee745f0863b1c233b8b7eb"), "website" : "1616.net" }
{ "_id" : ObjectId("4bee804ba23d558eb6687117"), "x" : 6, "name" : "caihuafeng1" }
{ "_id" : ObjectId("4bee804ba23d558eb6687118"), "x" : 6, "name" : "caihuafeng2" }
{ "_id" : ObjectId("4bee804ba23d558eb6687119"), "x" : 6, "name" : "caihuafeng3" }
{ "_id" : ObjectId("4bee804ba23d558eb668711a"), "x" : 6, "name" : "caihuafeng4" }
{ "_id" : ObjectId("4bee804ba23d558eb668711b"), "x" : 6, "name" : "caihuafeng5" }
{ "_id" : ObjectId("4bee804ba23d558eb668711c"), "x" : 6, "name" : "caihuafeng6" }
{ "_id" : ObjectId("4bee804ba23d558eb668711d"), "x" : 6, "name" : "caihuafeng7" }
{ "_id" : ObjectId("4bee804ba23d558eb668711e"), "x" : 6, "name" : "caihuafeng8" }
{ "_id" : ObjectId("4bee804ba23d558eb668711f"), "x" : 6, "name" : "caihuafeng9" }
{ "_id" : ObjectId("4bee804ba23d558eb6687120"), "x" : 6, "name" : "caihuafeng10" }
{ "_id" : ObjectId("4befb711b0e29ba1ce20e0bc"), "name" : "1616", "info" : { "url" : "http://www.1616.net/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb723b0e29ba1ce20e0bd"), "name" : "hao123", "info" : { "url" : "http://www.hao123.com/", "city" : "beijing" } }
{ "_id" : ObjectId("4befb740b0e29ba1ce20e0be"), "name" : "ll4la", "info" : { "url" : "http://www.114la.com/", "city" : "dongguan" } }
{ "_id" : ObjectId("4befc51ab0e29ba1ce20e0c2"), "firstname" : "cai", "lastname" : "huafeng" }

> db.data.ensureIndex({firstname: 1, lastname: 1}, {unique: true});
E11000 duplicate key error index: recommender.data.$firstname_1_lastname_1 dup key: { : null, : null }

6.删除索引
a.删除某个表中的所有索引

db.collection.dropIndexes();

b.删除某个表中的单一索引

db.collection.dropIndex({x: 1, y: -1})

> db.data.dropIndex({firstname: 1, lastname: 1});
{ "nIndexesWas" : 6, "ok" : 1 }

MongoDB学习（二）索引的用法

MongoDB中索引的用法

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