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📜  DocumentDB SQL-别名

📅  最后修改于: 2020-11-28 13:36:59             🧑  作者: Mango

在关系数据库中，SQL别名用于临时重命名表或列标题。同样，在DocumentDB中，别名用于临时重命名JSON文档，子文档，对象或任何字段。

重命名是一个临时更改，实际文档不会更改。基本上，创建别名是为了使字段/文档名称更具可读性。对于别名，使用AS关键字，它是可选的。

让我们考虑先前示例中使用的三个类似文档。

以下是AndersenFamily文档。

{ 
   "id": "AndersenFamily", 
   "lastName": "Andersen", 
    
   "parents": [ 
      { "firstName": "Thomas", "relationship":  "father" }, 
      { "firstName": "Mary Kay", "relationship":  "mother" } 
   ],
   
   "children": [ 
      { 
         "firstName": "Henriette Thaulow", 
         "gender": "female", 
         "grade": 5, 
         "pets": [ { "givenName": "Fluffy", "type":  "Rabbit" } ] 
      } 
   ],
   
   "location": { "state": "WA", "county": "King", "city": "Seattle" }, 
   "isRegistered": true 
}

以下是SmithFamily文档。

{ 
   "id": "SmithFamily",
    
   "parents": [ 
      { "familyName": "Smith", "givenName": "James" }, 
      { "familyName": "Curtis", "givenName": "Helen" }
   ],
   
   "children": [ 
      { 
         "givenName": "Michelle", 
         "gender": "female", 
         "grade": 1 
      },
        
      { 
         "givenName": "John", 
         "gender": "male", 
         "grade": 7,
            
         "pets": [ 
            { "givenName": "Tweetie", "type": "Bird" } 
         ] 
      } 
   ],
   
   "location": { 
      "state": "NY", 
      "county": "Queens", 
      "city": "Forest Hills" 
   },
   
   "isRegistered": true 
}

以下是WakefieldFamily文档。

{ 
   "id": "WakefieldFamily", 
    
   "parents": [ 
      { "familyName": "Wakefield", "givenName": "Robin" }, 
      { "familyName": "Miller", "givenName": "Ben" } 
   ],
   
   "children": [ 
      { 
         "familyName": "Merriam", 
         "givenName": "Jesse", 
         "gender": "female", 
         "grade": 6,
            
         "pets": [ 
            { "givenName": "Charlie Brown", "type": "Dog" }, 
            { "givenName": "Tiger", "type": "Cat" }, 
            { "givenName": "Princess", "type": "Cat" } 
         ] 
      },
        
      { 
         "familyName": "Miller", 
         "givenName": "Lisa", 
         "gender": "female", 
         "grade": 3, 
            
         "pets": [ 
            { "givenName": "Jake", "type": "Snake" } 
         ] 
      } 
   ],
   
   "location": { "state": "NY", "county": "Manhattan", "city": "NY" }, 
   "isRegistered": false 
}

让我们看一个讨论别名的例子。

别名

以下是将根连接到子级子文档的查询。我们有别名，例如f.id AS familyName，c.givenName AS childGivenName和c.firstName AS childFirstName。

SELECT  
   f.id AS familyName, 
   c.givenName AS childGivenName, 
   c.firstName AS childFirstName 
FROM Families f  
JOIN c IN f.children

执行上述查询后，将产生以下输出。

[ 
   { 
      "familyName": "WakefieldFamily", 
      "childGivenName": "Jesse" 
   },
    
   { 
      "familyName": "WakefieldFamily",
      "childGivenName": "Lisa" 
   },
    
   { 
      "familyName": "SmithFamily", 
      "childGivenName": "Michelle" 
   },
    
   { 
      "familyName": "SmithFamily", 
      "childGivenName": "John" 
   },
    
   { 
      "familyName": "AndersenFamily", 
      "childFirstName": "Henriette Thaulow" 
   } 
]

上面的输出显示了已更改的文件名，但这只是暂时的更改，原始文档没有被修改。