mongodb数据库中怎么使用索引
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在关系型数据库中索引可以加快对数据输出，非关系型数据库也是如此，可以减小磁盘IO访问，对大数据量有显著的效果。目前mongodb支持B-Tree,unique,sparse,hash索引
在mongodb集群中生成数据
[root@node2 mongodb-4.0.8]# ./bin/mongo --host 172.16.8.24 --port 27017
MongoDB shell version v4.0.8
connecting to: mongodb://172.16.8.24:27017/?gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("a1abbd3a-fe32-46ac-a959-4f8a62abd990") }
MongoDB server version: 4.0.8
Server has startup warnings:
wuhan:PRIMARY> for (var i=1;i<=1000;i++) { db.stu.insert({sn:i,name:"student"+i})}
WriteResult({ "nInserted" : 1 })
wuhan:PRIMARY> db.stu.find().count();
1000
wuhan:PRIMARY> db.stu.find();
{ "_id" : ObjectId("5ca3004015fc3dad4a419a75"), "sn" : 1, "name" : "student1" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a76"), "sn" : 2, "name" : "student2" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a77"), "sn" : 3, "name" : "student3" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a78"), "sn" : 4, "name" : "student4" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a79"), "sn" : 5, "name" : "student5" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a7a"), "sn" : 6, "name" : "student6" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a7b"), "sn" : 7, "name" : "student7" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a7c"), "sn" : 8, "name" : "student8" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a7d"), "sn" : 9, "name" : "student9" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a7e"), "sn" : 10, "name" : "student10" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a7f"), "sn" : 11, "name" : "student11" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a80"), "sn" : 12, "name" : "student12" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a81"), "sn" : 13, "name" : "student13" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a82"), "sn" : 14, "name" : "student14" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a83"), "sn" : 15, "name" : "student15" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a84"), "sn" : 16, "name" : "student16" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a85"), "sn" : 17, "name" : "student17" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a86"), "sn" : 18, "name" : "student18" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a87"), "sn" : 19, "name" : "student19" }
{ "_id" : ObjectId("5ca3004015fc3dad4a419a88"), "sn" : 20, "name" : "student20" }
Type "it" for more
wuhan:PRIMARY>
一.B-Tree索引的使用
1.单列索引使用
wuhan:PRIMARY> db.stu.ensureIndex({sn:1}) --在sn字段上创建索引
wuhan:PRIMARY> db.stu.find({sn:50}).explain(); --查看执行计划是否走索引
wuhan:PRIMARY> db.stu.getIndexKeys() --查看表中有多少键
[{"_id":1},{"sn":1}]
wuhan:PRIMARY> db.stu.getIndexes() --查看一个表所有索引
[{"v":2,"key":{"_id":1},"name":"_id_","ns":"tong.stu"},{"v":2,"key":{"sn":1},"name":"sn_1","ns":"tong.stu"}]
wuhan:PRIMARY> db.stu.dropIndex({sn:1}); --删除sn字段的索引
wuhan:PRIMARY> db.stu.dropIndexes(); --删除所有索引
2.多列索引使用
wuhan:PRIMARY> db.stu.ensureIndex({name:1},{name:"IX_name"}) --创建多列索引
{"createdCollectionAutomatically":false,"numIndexesBefore":1,"numIndexesAfter":2,"ok":1,"operationTime":Timestamp(1554188377,2),"$clusterTime":{"clusterTime":Timestamp(1554188377,2),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
wuhan:PRIMARY> db.stu.getIndexes() --查看索引信息
[{"v":2,"key":{"_id":1},"name":"_id_","ns":"tong.stu"},{"v":2,"key":{"name":1},"name":"IX_name","ns":"tong.stu"}]
wuhan:PRIMARY> db.stu.dropIndex({name:"IX_name"}) --删除其中一个索引
{"operationTime":Timestamp(1554188499,1),"ok":0,"errmsg":"can'tfindindexwithkey:{name:\"IX_name\"}","code":27,"codeName":"IndexNotFound","$clusterTime":{"clusterTime":Timestamp(1554188499,1),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
3.子文档索引使用
wuhan:PRIMARY> db.shop.insert({name:"Nokia",spc:{weight:120,area:"taiwan"}}) --写入数据
WriteResult({ "nInserted" : 1 })
wuhan:PRIMARY> db.shop.insert({name:"sanxing",spc:{weight:100,area:"hanguo"}}) --写入数据
WriteResult({ "nInserted" : 1 })
wuhan:PRIMARY> db.shop.find() --查询数据
{ "_id" : ObjectId("5ca337ff15fc3dad4a419e5d"), "name" : "Nokia", "spc" : { "weight" : 120, "area" : "taiwan" } }
{ "_id" : ObjectId("5ca3382c15fc3dad4a419e5e"), "name" : "sanxing", "spc" : { "weight" : 100, "area" : "hanguo" } }
wuhan:PRIMARY> db.shop.find({"spc.area":"hanguo"}); --查询子文档的数据
{ "_id" : ObjectId("5ca3382c15fc3dad4a419e5e"), "name" : "sanxing", "spc" : { "weight" : 100, "area" : "hanguo" } }
wuhan:PRIMARY> db.shop.ensureIndex({"spc.area":1}); --子文档创建索引
{"createdCollectionAutomatically":false,"numIndexesBefore":1,"numIndexesAfter":2,"ok":1,"operationTime":Timestamp(1554200928,2),"$clusterTime":{"clusterTime":Timestamp(1554200928,2),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
wuhan:PRIMARY> db.shop.getIndexes();
[{"v":2,"key":{"_id":1},"name":"_id_","ns":"tong.shop"},{"v":2,"key":{"spc.area":1},"name":"spc.area_1","ns":"tong.shop"}]
wuhan:PRIMARY>
二.唯一索引(唯一索引中字段值必须是唯一的)
wuhan:PRIMARY> db.stu.ensureIndex({name:1},{unique:true})
{"createdCollectionAutomatically":false,"numIndexesBefore":1,"numIndexesAfter":2,"ok":1,"operationTime":Timestamp(1554188549,2),"$clusterTime":{"clusterTime":Timestamp(1554188549,2),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
wuhan:PRIMARY> db.stu.getIndexes()
[{"v":2,"key":{"_id":1},"name":"_id_","ns":"tong.stu"},{"v":2,"unique":true,"key":{"name":1},"name":"name_1","ns":"tong.stu"}]
wuhan:PRIMARY> db.stu.totalIndexSize() --查看索引大小
40960
wuhan:PRIMARY> db.stu.totalSize()
69632
wuhan:PRIMARY>
三.稀疏索引(字段有值就创建索引,没有值不创建索引)
wuhan:PRIMARY> db.shop.find()
{ "_id" : ObjectId("5ca337ff15fc3dad4a419e5d"), "name" : "Nokia", "spc" : { "weight" : 120, "area" : "taiwan" } }
{ "_id" : ObjectId("5ca3382c15fc3dad4a419e5e"), "name" : "sanxing", "spc" : { "weight" : 100, "area" : "hanguo" } }
wuhan:PRIMARY> db.shop.insert({}) --插入一个空值
WriteResult({ "nInserted" : 1 })
wuhan:PRIMARY> db.shop.find();
{ "_id" : ObjectId("5ca337ff15fc3dad4a419e5d"), "name" : "Nokia", "spc" : { "weight" : 120, "area" : "taiwan" } }
{ "_id" : ObjectId("5ca3382c15fc3dad4a419e5e"), "name" : "sanxing", "spc" : { "weight" : 100, "area" : "hanguo" } }
{ "_id" : ObjectId("5ca3419c15fc3dad4a419e5f") }
wuhan:PRIMARY> db.shop.ensureIndex({name:1},{sparse:true}); --创建稀疏索引
{"createdCollectionAutomatically":false,"numIndexesBefore":2,"numIndexesAfter":3,"ok":1,"operationTime":Timestamp(1554203093,2),"$clusterTime":{"clusterTime":Timestamp(1554203093,2),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
wuhan:PRIMARY> db.shop.find({name:"null"}); --null值不显示
wuhan:PRIMARY>
四.哈稀索引
wuhan:PRIMARY> db.t.ensureIndex({a:"hashed"});
{"createdCollectionAutomatically":false,"numIndexesBefore":1,"numIndexesAfter":2,"ok":1,"operationTime":Timestamp(1554203661,2),"$clusterTime":{"clusterTime":Timestamp(1554203661,2),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
wuhan:PRIMARY> db.t.find({a:"25"}).explain();
{"queryPlanner":{"plannerVersion":1,"namespace":"tong.t","indexFilterSet":false,"parsedQuery":{"a":{"$eq":"25"}},"winningPlan":{"stage":"FETCH","filter":{"a":{"$eq":"25"}},"inputStage":{"stage":"IXSCAN","keyPattern":{"a":"hashed"},"indexName":"a_hashed",--显示为hash索引"isMultiKey":false,"isUnique":false,"isSparse":false,"isPartial":false,"indexVersion":2,"direction":"forward","indexBounds":{"a":["[7200060250846542811,7200060250846542811]"]}}},"rejectedPlans":[]},"serverInfo":{"host":"node2","port":27017,"version":"4.0.8","gitVersion":"9b00696ed75f65e1ebc8d635593bed79b290cfbb"},"ok":1,"operationTime":Timestamp(1554203690,1),"$clusterTime":{"clusterTime":Timestamp(1554203690,1),"signature":{"hash":BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),"keyId":NumberLong(0)}}}
wuhan:PRIMARY>
五.索引重建(当索引效率不高时可以考虑重建索引)
wuhan:PRIMARY> db.t.reIndex(); --重建t表的索引
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