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本篇文章為大家展示了MongoDB數據庫中如何使用索引，內容簡明扼要并且容易理解，絕對能使你眼前一亮，通過這篇文章的詳細介紹希望你能有所收獲。
MongoDB的各種索引有哪些用法
1.單列索引
在字段x上創建索引，1 (ascending) or -1 (descending)
> db.data.ensureIndex({x:1})
顯示表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為6的值，此時已經用到索引了
> 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.默認索引
上述1中db.data.getIndexes()顯示出來的一共有2個索引，其中_id是創建表的時候自動創建的索引，此索引是不能夠刪除的。
An index is always created on _id. This index is special and cannot be deleted. The _id index enforces uniqueness for its keys.
3.文檔作為索引的鍵值
a.單列索引
MongoDB的官方文檔上面是這樣說的:
Documents as Keys
Indexed fields may be of any type, including documents:
往數據庫recommender的表data中插入三條記錄
> 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"}});
對字段info創建索引
> db.data.ensureIndex({info: 1});
顯示表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"
}
]
查找指定的記錄，此時會用到索引
> 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.組合索引
建立組合索引
> 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"
}
]
下面幾個操作均會用到索引
> 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" } }
MongoDB的各種索引有哪些用法
4.組合索引
注意，這里的組合索引與上述3中的b中的組合索引是有點不同的，4里面是對一級字段建立組合索引，而上述3中是對二級字段建立組合索引。
在字段name及info上面創建組合索引
> db.data.ensureIndex({name: 1, info: -1});
當創建組合索引時，字段后面的1表示升序，-1表示降序，是用1還是用-1主要是跟排序的時候或指定范圍內查詢的時候有關的，具體看下面的英文原文的說明。
When creating an index, the number associated with a key specifies the direction of the index, so it should always be 1 (ascending) or -1 (descending). Direction doesn’t matter for single key indexes or for random access retrieval but is important if you are doing sorts or range queries on compound indexes.
顯示所有的索引
> 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"
}
]
下面的排序將用到上面的索引
最后一行的”name” : “ll4la”實際上是”name” : “114la”(就是將數字一寫成了字母l)，但是我錄入的時候寫成了”name” : “ll4la”，是我寫錯了，但是排序的結果是對的。
> 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" } }
MongoDB組合索引規則
If you have a compound index on multiple fields, you can use it to query on the beginning subset of fields. So if you have an index on
a,b,c
you can use it query on
a
a,b
a,b,c
如果用過MySQL的話，看起來是不是很熟悉，原理跟MySQL是一樣的。
5.唯一索引
往表data中插入一條記錄。
> db.data.insert({firstname: "cai", lastname: "huafeng"});
由于表data中只有一記錄有字段firstname及lastname，其它的行均沒有相應的值，也就是均為null，為null就說明是相同的，而唯一索引是不允許有相同的值的，所以下面創建唯一組合索引時報錯了。
所以建立唯一索引時，不管是對單個字段還是多個字段建立索引，則最好每一行均有此字段，否則會報錯。
> 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.$firstname_1_lastname_1 dup key: { : null, : null }
下面我們用另外一個表person來進行測試
> db.person.ensureIndex({firstname:1, lastname: 1},{unique: true});
> db.person.insert({firstname: 'cai', lastname: 'huafeng'});
第二次插入同樣值的時候報錯了，說明唯一索引生效了，其實跟MySQL里面是一樣的。
> db.person.insert({firstname: 'cai', lastname: 'huafeng'});
E11000 duplicate key error index: recommender.person.$firstname_1_lastname_1 dup key: { : "cai", : "huafeng" }
6.唯一索引中的重復值處理
刪除上述5中的索引，插入兩行一樣的記錄
> db.person.dropIndexes();
{
"nIndexesWas" : 2,
"msg" : "non-_id indexes dropped for collection",
"ok" : 1
}
> db.person.find();
{ "_id" : ObjectId("4befcda6b0e29ba1ce20e0cf"), "firstname" : "cai", "lastname" : "huafeng" }
> db.person.insert({firstname: 'cai', lastname: 'huafeng'});
> db.person.find();
{ "_id" : ObjectId("4befcda6b0e29ba1ce20e0cf"), "firstname" : "cai", "lastname" : "huafeng" }
{ "_id" : ObjectId("4befcef0b0e29ba1ce20e0d1"), "firstname" : "cai", "lastname" : "huafeng" }
如果現在直接在字段firstname及lastname上面創建唯一組合索引的時候肯定會報錯，我們來試一試:
> db.person.ensureIndex({firstname: 1, lastname: 1}, {unique: true});
E11000 duplicate key error index: recommender.person.$firstname_1_lastname_1 dup key: { : "cai", : "huafeng" }
查看表person的索引，我們可以看到，新創建的索引沒有生成。
> db.person.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.person",
"key" : {
"_id" : 1
}
}
]
可以在第二個json對象加入一項dropDups: true，這樣在創建唯一組合索引的時候不會報錯，保留文檔中第一個重復的值，其它重復的值均刪除。
再次測試一下，加入dropDups選項，雖然報錯了，但是唯一組合索引已經建立了。
> db.person.ensureIndex({firstname: 1, lastname: 1}, {unique: true, dropDups: true});
E11000 duplicate key error index: recommender.person.$firstname_1_lastname_1 dup key: { : "cai", : "huafeng" }
> db.person.getIndexes();
[
{
"name" : "_id_",
"ns" : "recommender.person",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4befcfd9b0e29ba1ce20e0d3"),
"ns" : "recommender.person",
"key" : {
"firstname" : 1,
"lastname" : 1
},
"name" : "firstname_1_lastname_1",
"unique" : true,
"dropDups" : true
}
]
再次查詢表person中的記錄，發現重復的記錄已經自動刪除了。
> db.person.find();
{ "_id" : ObjectId("4befcda6b0e29ba1ce20e0cf"), "firstname" : "cai", "lastname" : "huafeng" }
MongoDB官方文檔的說明
A unique index cannot be created on a key that has duplicate values. If you would like to create the index anyway, keeping the first document the database indexes and deleting all subsequent documents that have duplicate values, add the dropDups option.
db.things.ensureIndex({firstname : 1}, {unique : true, dropDups : true})
7.刪除索引
a.刪除某個表中的所有索引
To delete all indexes on the specified collection:
db.collection.dropIndexes();
b.刪除某個表中的單一索引
To delete a single index:
db.collection.dropIndex({x: 1, y: -1})
> db.data.dropIndex({firstname: 1, lastname: 1});
{ "nIndexesWas" : 6, "ok" : 1 }
Running directly as a command without helper:
// note: command was "deleteIndexes", not "dropIndexes", before MongoDB v1.3.2
// remove index with key pattern {y:1} from collection foo
db.runCommand({dropIndexes:'foo', index : {y:1}})
// remove all indexes:
db.runCommand({dropIndexes:'foo', index : '*'})
> db.person.ensureIndex({firstname: 1, lastname: 1});
> db.runCommand({dropIndexes:'person', index:{firstname:1, lastname:1}});
{ "nIndexesWas" : 2, "ok" : 1 }
上述內容就是MongoDB數據庫中如何使用索引，你們學到知識或技能了嗎？如果還想學到更多技能或者豐富自己的知識儲備，歡迎關注億速云行業資訊頻道。
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