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小編給大家分享一下MongoDB中索引怎么用，相信大部分人都還不怎么了解，因此分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后大有收獲，下面讓我們一起去了解一下吧！
在任何數據庫之中，索引都是一種提升數據庫檢索性能的手段。
MongoDB數據庫里面依然會存在兩種索引創建：一種是自動創建，另外一種是手工創建。
范例：重新準備一個新的簡單集合。
db.emp.drop();
db.emp.insert({"name":"趙一","sex":"男","age":30,"sal":1000,"loc":"北京"});
db.emp.insert({"name":"錢二","sex":"女","age":22,"sal":5000,"loc":"上海"});
db.emp.insert({"name":"孫三","sex":"男","age":40,"sal":2000,"loc":"深圳"});
db.emp.insert({"name":"李四","sex":"女","age":30,"sal":7000,"loc":"北京"});
db.emp.insert({"name":"周五","sex":"女","age":30,"sal":6400,"loc":"北京"});
db.emp.insert({"name":"吳六","sex":"男","age":30,"sal":2500,"loc":"重慶"});
db.emp.insert({"name":"鄭七","sex":"女","age":50,"sal":4700,"loc":"成都"});
db.emp.insert({"name":"王八","sex":"男","age":35,"sal":8000,"loc":"北京"});
此時在emp的集合上并沒有去設置任何的索引，可以通過getIndexes()函數來觀察在emp集合中的索引。
范例：查詢默認狀態下emp集合的索引內容
> db.emp.getIndexes();
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "hr.emp"
}
]
現在發現會存在有一個“_id”列的索引內容。但是如果要想創建自己的索引，則可以使用如下的語法：
索引創建：db.集合名稱.createIndex({列:1})
設置的1表示索引按照升序的方式進行排序，如果使用降序則使用“-1”
范例：創建一個索引，在age字段上設置一個降序索引
> db.emp.createIndex({"age":-1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
此時并沒有設置索引的名字，所以名字是自動命名的。命名的規范：“字段名稱_索引的排序模式”
> db.emp.getIndexes();
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "hr.emp"
},
{
"v" : 2,
"key" : {
"age" : -1
},
"name" : "age_-1",
"ns" : "hr.emp"
}
]
范例：針對于當前的age字段上的索引做一個分析
> db.emp.find({"age":30}).explain("executionStats");
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "hr.emp",
"indexFilterSet" : false,
"parsedQuery" : {
"age" : {
"$eq" : 30
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"age" : -1
},
"indexName" : "age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
]
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 4,
"executionTimeMillis" : 0,
"totalKeysExamined" : 4,
"totalDocsExamined" : 4,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 4,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 4,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 4,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 4,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 4,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"age" : -1
},
"indexName" : "age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
]
},
"keysExamined" : 4,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
"serverInfo" : {
"host" : "D2-LZY245",
"port" : 27017,
"version" : "3.4.7",
"gitVersion" : "cf38c1b8a0a8dca4a11737581beafef4fe120bcd"
},
"ok" : 1
}
此時的查詢使用了索引的技術，但是下面再來觀察一個查詢，不使用索引字段
范例：針對于sal字段進行查詢
> db.emp.find({"sal":{"$gt":5000}}).explain("executionStats");
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "hr.emp",
"indexFilterSet" : false,
"parsedQuery" : {
"sal" : {
"$gt" : 5000
}
},
"winningPlan" : {
"stage" : "COLLSCAN",
"filter" : {
"sal" : {
"$gt" : 5000
}
},
"direction" : "forward"
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 3,
"executionTimeMillis" : 0,
"totalKeysExamined" : 0,
"totalDocsExamined" : 8,
"executionStages" : {
"stage" : "COLLSCAN",
"filter" : {
"sal" : {
"$gt" : 5000
}
},
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 10,
"advanced" : 3,
"needTime" : 6,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"direction" : "forward",
"docsExamined" : 8
}
},
"serverInfo" : {
"host" : "D2-LZY245",
"port" : 27017,
"version" : "3.4.7",
"gitVersion" : "cf38c1b8a0a8dca4a11737581beafef4fe120bcd"
},
"ok" : 1
}
此時在sal字段上并沒有設置索引，所以當前的索引形式就變成了全集合掃描的模式。
但是如果說，現在換一種形式，年齡和薪水一起執行查詢：
> db.emp.find({"age":30,"sal":7000}).explain("executionStats")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "hr.emp",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"age" : {
"$eq" : 30
}
},
{
"sal" : {
"$eq" : 7000
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"sal" : {
"$eq" : 7000
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"age" : -1
},
"indexName" : "age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
]
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 0,
"totalKeysExamined" : 4,
"totalDocsExamined" : 4,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"sal" : {
"$eq" : 7000
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 1,
"needTime" : 3,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 4,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 4,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 4,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"age" : -1
},
"indexName" : "age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
]
},
"keysExamined" : 4,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
"serverInfo" : {
"host" : "D2-LZY245",
"port" : 27017,
"version" : "3.4.7",
"gitVersion" : "cf38c1b8a0a8dca4a11737581beafef4fe120bcd"
},
"ok" : 1
}
這個時候雖然age字段上面存在索引，由于sal字段上面沒有索引，所以依然使用的是全表掃描操作。為了解決此時的問題，可以使用一個復合索引。
> db.emp.createIndex({"age":-1,"sal":-1},{name:"age_-1_sal_-1_index"})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 2,
"numIndexesAfter" : 3,
"ok" : 1
}
范例：默認使用索引
> db.emp.find({"age":30,"sal":7000}).explain("executionStats")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "hr.emp",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"age" : {
"$eq" : 30
}
},
{
"sal" : {
"$eq" : 7000
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"age" : -1,
"sal" : -1
},
"indexName" : "age_-1_sal_-1_index",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ],
"sal" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
],
"sal" : [
"[7000.0, 7000.0]"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "FETCH",
"filter" : {
"sal" : {
"$eq" : 7000
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"age" : -1
},
"indexName" : "age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
]
}
}
}
]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 0,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 1,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"age" : -1,
"sal" : -1
},
"indexName" : "age_-1_sal_-1_index",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ],
"sal" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[30.0, 30.0]"
],
"sal" : [
"[7000.0, 7000.0]"
]
},
"keysExamined" : 1,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
"serverInfo" : {
"host" : "D2-LZY245",
"port" : 27017,
"version" : "3.4.7",
"gitVersion" : "cf38c1b8a0a8dca4a11737581beafef4fe120bcd"
},
"ok" : 1
}
但是如果換到了以下條件：
> db.emp.find({"$or":[{"age":{"$gt":30}},{"sal":{"$gt":5000}}]}).explain("executionStats")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "hr.emp",
"indexFilterSet" : false,
"parsedQuery" : {
"$or" : [
{
"age" : {
"$gt" : 30
}
},
{
"sal" : {
"$gt" : 5000
}
}
]
},
"winningPlan" : {
"stage" : "SUBPLAN",
"inputStage" : {
"stage" : "COLLSCAN",
"filter" : {
"$or" : [
{
"age" : {
"$gt" : 30
}
},
{
"sal" : {
"$gt" : 5000
}
}
]
},
"direction" : "forward"
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 5,
"executionTimeMillis" : 0,
"totalKeysExamined" : 0,
"totalDocsExamined" : 8,
"executionStages" : {
"stage" : "SUBPLAN",
"nReturned" : 5,
"executionTimeMillisEstimate" : 0,
"works" : 10,
"advanced" : 5,
"needTime" : 4,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"inputStage" : {
"stage" : "COLLSCAN",
"filter" : {
"$or" : [
{
"age" : {
"$gt" : 30
}
},
{
"sal" : {
"$gt" : 5000
}
}
]
},
"nReturned" : 5,
"executionTimeMillisEstimate" : 0,
"works" : 10,
"advanced" : 5,
"needTime" : 4,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"direction" : "forward",
"docsExamined" : 8
}
}
},
"serverInfo" : {
"host" : "D2-LZY245",
"port" : 27017,
"version" : "3.4.7",
"gitVersion" : "cf38c1b8a0a8dca4a11737581beafef4fe120bcd"
},
"ok" : 1
}
現在發現并沒有使用索引，所以這個時候看能否強制使用一次索引：hint()函數為強制使用索引操作。
范例：強制使用索引
> db.emp.find({"$or":[{"age":{"$gt":50}},{"sal":{"$gt":3000}}]}).hint("age_-1_sal_-1_index").explain("executionStats")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "hr.emp",
"indexFilterSet" : false,
"parsedQuery" : {
"$or" : [
{
"age" : {
"$gt" : 50
}
},
{
"sal" : {
"$gt" : 3000
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"$or" : [
{
"age" : {
"$gt" : 50
}
},
{
"sal" : {
"$gt" : 3000
}
}
]
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"age" : -1,
"sal" : -1
},
"indexName" : "age_-1_sal_-1_index",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ],
"sal" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[MaxKey, MinKey]"
],
"sal" : [
"[MaxKey, MinKey]"
]
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 5,
"executionTimeMillis" : 0,
"totalKeysExamined" : 8,
"totalDocsExamined" : 8,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"$or" : [
{
"age" : {
"$gt" : 50
}
},
{
"sal" : {
"$gt" : 3000
}
}
]
},
"nReturned" : 5,
"executionTimeMillisEstimate" : 0,
"works" : 9,
"advanced" : 5,
"needTime" : 3,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 8,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 8,
"executionTimeMillisEstimate" : 0,
"works" : 9,
"advanced" : 8,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"age" : -1,
"sal" : -1
},
"indexName" : "age_-1_sal_-1_index",
"isMultiKey" : false,
"multiKeyPaths" : {
"age" : [ ],
"sal" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"age" : [
"[MaxKey, MinKey]"
],
"sal" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 8,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
"serverInfo" : {
"host" : "D2-LZY245",
"port" : 27017,
"version" : "3.4.7",
"gitVersion" : "cf38c1b8a0a8dca4a11737581beafef4fe120bcd"
},
"ok" : 1
}
如果正常來講，這個代碼根本就不可能調用默認的索引執行，如果需要可以使用hint()函數強制MongoDB必須使用索引。
如果在一個集合里面設置了過多的索引，實際上會導致性能下降。那么可以刪除索引。
范例：刪除一個索引
> db.emp.dropIndex("age_-1_sal_-1_index")
{ "nIndexesWas" : 3, "ok" : 1 }
> db.emp.getIndexes();
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "hr.emp"
},
{
"v" : 2,
"key" : {
"age" : -1
},
"name" : "age_-1",
"ns" : "hr.emp"
}
]
范例：刪除非"_id"的索引，也就是自定義的索引
> db.emp.dropIndexes();
{
"nIndexesWas" : 2,
"msg" : "non-_id indexes dropped for collection",
"ok" : 1
}
> db.emp.getIndexes();
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "hr.emp"
}
]
以上是“MongoDB中索引怎么用”這篇文章的所有內容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內容對大家有所幫助，如果還想學習更多知識，歡迎關注億速云行業資訊頻道！
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