# Query

## **常見名詞**

|   Node   | 具有ES功能的Server |
| :------: | :-----------: |
|  Cluster |     很多Node    |
|   Index  |       DB      |
|   Type   |     Table     |
|   Field  |  欄位(Columns)  |
| Document |   一筆資料(Row)   |
|   Shard  |   組成Index的部分  |

## **Index建立、文章新增**

```python
#連線server
es=Elasticsearch([{'host': 'localhost', 'port': 9200}])

#如果需要身分驗證
es=Elasticsearch(['ip&port'],http_auth=('username','password'))


#建立index
#若連線狀態是ignore則回傳錯誤訊息
#建立時可在body加上表格欄位設定(table_format)，也就是mapping設定
#其中article即doc_type
table_format={
        "mappings":{
            "article":{
                "properties":{
                    "title":{
                        "type":"string",
                        "index":"not_analyzed"
                    },
                    "content" : {
                        "type":"string",
                        "index":"not_analyzed"
                    }
                }
            }
        }
    }
res=es.indices.create(index=index_name, ignore=[400,409,404], body=table_format)


#判斷index是否存在，會回傳boolean
res=es.indices.exists(index='index_name')


#新增資料至doc_type中
#id可以是任意字串
# index :若已存在則覆蓋
# create:若已存在則error
res=es.create(index='index_name', doc_type='article', id='aid', body=data)
res=es.index(index='index_name', doc_type='article', id='aid', body=data)
```

## mapping 映射

資料型態

text vs keyword

text：結構較複雜的資料，如：文章、句子。適用於full-text search

keyword：結構較簡單的資料，如：email、品牌型號。適用完全比對的需求

## score 相關性

主要根據TF/IDF!? (gitbook 7-3, 8-3)

影響因素：字串與字串之間的距離；字串出現的次數；配對成功的句子長度

## 查詢語法

## match

回傳結果包含\_score排名(怪怪ㄉ)，英文大小寫**有影響**

若搜尋字串無法完全比對，會根據**部分搜尋字串**進行比對，也就是搜尋字串會被拆解

```python
#gitbook 7-4
query={
    'query': {
      'match': {
        'about':'Sony'
       }
    }
}
res=es.search(index='indexname',doc_type='typename',body=query) #搜尋about欄位包含sony的結果
```

## match\_phrase

結果同樣包含\_score排名，會**完全比對**搜尋字串，也就是欄位中一定要出現"很好用"

如資料以陣列儲存則需要與陣列元素完全相同

```python
#gitbook 7-4
qs={
    "query" : {
        "match_phrase" : {
            "about" : "很好用"
        }
    }
}
```

## term

完全比對日期、數值與字串，比對字串記得將mapping中的字串欄位改為"index":"not\_analyzed"

```python
#gitbook 7-4
qs={
    "query" : {
        "term" : {
            "interests" : "workout"
        }
    }
}
```

## terms

可使用多個比對對條件，符合其中一個即可

```python
#gitbook 7-4
#interest包含workout'或'jogging
qs={
    "query" : {
        "terms" : {
            "interests" : ["workout","jogging"]
        }
    }
}
```

## aggregations

```python
#將interests的內容進行聚合
qs={
  "aggs": {
    "search_all_interests": { #query名稱
      "terms": { "field": "interests" }
    }
  }
}

#聚合first_name叫做Pan的員工的所有interest
qs={
  "query": {
    "match": {
      "first_name": "Pan"
    }
  },
  "aggs": {
    "all_interests": {
      "terms": {
        "field": "interests"
      }
    }
  }
}
```

## 組合查詢

must：and

must\_not：not

should：or

```python
#gitbook 12-2
#interests中不包含sony的結果
qs={
  "query" : {
      "bool":{
        "must_not":{
           "term":{
             "interests":"sony"
           }
         }
      }
   }
}


#與aggs結合，聚合interests中非sony的所有結果
qs={
  "query" : {
    "bool":{
      "must_not":{
        "term":{
          "interests":"sony"
        }
      }
    }
  },
  "aggs": {
    "all_interests": {
      "terms": {
        "field": "interests"
      }
    }
  }
}
```

## Range

| gt : 大於 | gte：大於等於 |
| :-----: | :------: |
|  lt：小於  | lte：小於等於 |

```python
#gitbook 12-5
#不用加filter
#price介於2000~5000
{
    "range" : {
        "price" : { #欄位名稱
            "gte" : 5000, #大於等於
            "lt" : 20000  #小於等於
        }
    }
}
```

### 巢狀判斷式

<https://www.elastic.co/blog/lost-in-translation-boolean-operations-and-filters-in-the-bool-query>

判斷是否連線成功

```python
if not es.ping():
    raise ValueError("Connection failed")
```

api doc：<http://elasticsearch-py.readthedocs.io/en/master/api.html#elasticsearch>

中文GITBOOK：<https://es.xiaoleilu.com/index.html>


---

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