# 建立索引，優化查詢速度

# 檢視索引
> db.enter_room.getIndexes()
[
    {
        "v" : 2,
        "key" : {
            "_id" : 1
        },
        "name" : "_id_",
        "ns" : "room.enter_room"
    }
]


# 建立索引
> db.enter_room.ensureIndex({room_id: 1, user_id: 1}, {background: true})
{
    "createdCollectionAutomatically
 
" : false,
    "numIndexesBefore" : 1,
    "numIndexesAfter" : 2,
    "ok" : 1
}


# 檢視索引
> db.enter_room.getIndexes()
[
    {
        "v" : 2,
        "key" : {
            "_id" : 1
        },
        "name" : "_id_",
        "ns" : "room.enter_room"
    },
    {
        "v" : 2,
        "key" : {
            
 
"room_id" : 1,
            "user_id" : 1
        },
        "name" : "room_id_1_user_id_1",
        "ns" : "room.enter_room",
        "background" : true
    }
]



# 集合內資料
> db.enter_room.findOne()
{
    "_id" : ObjectId("606c195c8340b651d1084d9b"),
    "enter_time" : "2021-04-06 16:18:10",
    "room_id
 
" : "123845",
    "user_id" : "1385786",
    "user_count" : "12"
}