# MongoDB教育訓練-07
- 只能保證分片唯一，不能保證全局唯一
- sparse index : 欄位可能不存在document中使用
- partial index : 依據欄位的值決定要不要放入索引（刪除的不放）
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/wWPaTmNWtK43dfFl-image-1639709435352.png)
- hashed indexes : md5 取前20個byte，並不可作為唯一索引，使用時機：控制索引大小（如url）
- 關於時間不適合，會造成分散在所有分片
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/BNDz6MjJGH4XQVMy-image-1639709740460.png)
- 索引增加讀的效能，減低寫的效能
- 建議每張表的索引< 10
- 新增資料會做索引異動，更新不會(但更新欄位會)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/p9ksssT9foFnXp7U-image-1639710154313.png)
索引越大，記憶體越大
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/4zOuCSYrDtGgfnf8-image-1639710316926.png)
### 前綴壓縮
- App le
- App le iphon
- App le store
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/rrhpi4p8v1TQjucP-image-1639710384084.png)
### Multikey indexs
建在array上的index (是不是由系統判斷)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/4jvxLsF5Zv6B6JrQ-image-1639710538365.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/xbwrPXNGHcrCzpeC-image-1639710636236.png)
通常使用"comments.rating" : 1 這種索引
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/kQG5DV39z1YWECuY-image-1639710866463.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/EMgtxyUFyCFNrcC0-image-1639711096453.png)
### Compound符合索引
多欄位索引 (欄位A & 欄位B 查詢適用 )
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/1fStpr6XArU4nsF0-image-1639711185981.png)
### Compound Indexes 複合索引
- MongoDB 通常使用一個索引作查詢
- 最多可以做32個
- 順序很重要
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/bFZZMWa76Rs0PgBT-image-1639711281834.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/gWtjM19sgBjXu1vs-image-1639711459539.png)
欄位順序必須相同
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/FPft7ie7e0KvO9md-image-1639711603003.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/EbJ0MfYoAaSPFIRg-image-1639711744724.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/V53vAeoi5saMlNUs-image-1639711763345.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/NXkdKdxjZW2po5PQ-image-1639711833183.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/MiTyDRZgKHj8WhZM-image-1639711867625.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/PO3Xs0ElcRvrZxDH-image-1639711980197.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/omFQETIWY1NDNVfY-image-1639712284049.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/PjRvnyiSx4W82DeT-image-1639712401606.png)
### ＥＳＲ原則
等值 排序 範圍
10000以內不算數據量大
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/X2qvWrX7SXv1CsYz-image-1639712527794.png)
兩欄位都是陣列，禁止使用，因為所有數量是陣列的乘積
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/7gfZXdRRZGTKJXQj-image-1639712629336.png)
###
#### index 完全覆蓋查詢(資料都從index返回，不用直接查詢document)
\_id 不要出現, multikey 不適用
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/U5rt5J6oLLv4cPWC-image-1639712718185.png)
[](https://bookstack.treemanou.com/uploads/images/gallery/2021-12/QwW6VDciHMXheDrv-image-1639712827734.png)
```shell
db.listingsAndReviews.find({amenities:"Waterfront","bed_type":{$in:["Futon","Real Bed"]}})
.projection({bedrooms:1, price:1,_id:0,"address.country":1}).explain("executionStats")
db.listingsAndReviews.createIndex({amenities:1, bedrooms:-1,price:11,bed_type:1,first_review:1,last_review:1})
```