MongoDb索引操作

> use user  
switched to db user  
> show collections  
system.indexes  
u_info  
u_setting  
> db.system.indexes.find(); 这是默认的索引（默认为_id为索引）  
{ "name" : "\_id\_", "ns" : "user.u\_info", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "name" : "\_id\_", "ns" : "user.u\_setting", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
>  
> db.u_info.insert({uid:1,name:"Falcon.C",address:"Beijing"});  
> db.u_info.insert({uid:2,name:"sexMan",address:"Wuhan"});  
> db.u_info.find();  
{ "_id" : ObjectId("4b9cf280c84d7f20576c4df2"), "uid" : 1, "name" : "Falcon.C", "address" : "Beijing" }  
{ "_id" : ObjectId("4b9cf284c84d7f20576c4df3"), "uid" : 2, "name" : "sexMan", "address" : "Wuhan" }  
插入了2条记录，我们来把uid设置为索引字段：  
> db.u_info.ensureIndex({uid:1});  
> db.u_info.ensureIndex({name:1});  
> db.system.indexes.find();  
{ "name" : "\_id\_", "ns" : "user.u\_info", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "name" : "\_id\_", "ns" : "user.u\_setting", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "ns" : "user.u\_info", "key" : { "uid" : 1 }, "name" : "uid\_1" }  
{ "ns" : "user.u\_info", "key" : { "name" : 1 }, "name" : "name\_1" }  
>  
#这时我们看到多了刚才我们设置的那个字段，这样在查询的时候，如果查询条件有uid字段或name字段，则走索引来进行查询  
有索引：  
> db.u_info.find({name:"Falcon.C"});  
{ "_id" : ObjectId("4b9cf280c84d7f20576c4df2"), "uid" : 1, "name" : "Falcon.C", "address" : "Beijing" }  
> db.u_info.find({name:"Falcon.C"}).explain();  
{   
    "cursor" : "BtreeCursor name_1",   
    "startKey" : {   
        "name" : "Falcon.C"   
    },   
    "endKey" : {   
        "name" : "Falcon.C"   
    },   
    "nscanned" : 1,   
    "n" : 1,   
    "millis" : 0,   
    "allPlans" : [   
        {   
            "cursor" : "BtreeCursor name_1",   
            "startKey" : {   
                "name" : "Falcon.C"   
            },   
            "endKey" : {   
                "name" : "Falcon.C"   
            }   
        }   
    ]  
}  
删除索引后：  
> db.system.indexes.find();  
{ "name" : "\_id\_", "ns" : "user.u\_info", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "name" : "\_id\_", "ns" : "user.u\_setting", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "ns" : "user.u\_info", "key" : { "uid" : 1 }, "name" : "uid\_1" }  
{ "ns" : "user.u\_info", "key" : { "name" : 1 }, "name" : "name\_1" }  
> db.u\_info.dropIndex("name\_1")  
{ "nIndexesWas" : 3, "ok" : 1 }  
> db.u_info.find({name:"Falcon.C"}).explain();  
{   
    "cursor" : "BasicCursor",   
    "startKey" : {   
    },   
    "endKey" : {   
    },   
    "nscanned" : 2,   
    "n" : 1,   
    "millis" : 0,   
    "allPlans" : [   
        {   
            "cursor" : "BasicCursor",   
            "startKey" : {   
            },   
            "endKey" : {   
            }   
        }   
    ]  
}  
> db.system.indexes.find();  
{ "name" : "\_id\_", "ns" : "user.u\_info", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "name" : "\_id\_", "ns" : "user.u\_setting", "key" : { "\_id" : ObjectId("000000000000000000000000") } }  
{ "ns" : "user.u\_info", "key" : { "uid" : 1 }, "name" : "uid\_1" }