DocumentDB SQL - 值关键字

当你了解到自己只返回一个值时,VALUE 关键字就可以通过避免创建成熟对象而帮助生成瘦身结果集。 VALUE 关键字提供了一个返回 JSON 值的方法。

让我们看一个简单的例子。

下面是具有 VALUE 关键字的查询。

SELECT VALUE "Hello World, this is DocumentDB SQL Tutorial"

当执行此查询时,它返回标量"Hello World, this is DocumentDB SQL Tutorial"。

[ 
   "Hello World, this is DocumentDB SQL Tutorial" 
]

在另一个示例中,让我们考虑前一个示例中的三个文档。

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 
}	  

以下是查询。

SELECT VALUE f.location 
FROM Families f

当执行此查询时,它会返回没有位置标签的地址。

[ 
   { 
      "state": "NY", 
      "county": "Manhattan", 
      "city": "NY" 
   }, 
	
   { 
      "state": "NY", 
      "county": "Queens", 
      "city": "Forest Hills" 
   },
	
   { 
      "state": "WA", 
      "county": "King", 
      "city": "Seattle" 
   } 
] 

如果我们现在不使用 VALUE Keyword 指定相同的查询,则它将返回带有位置标签的地址。以下是查询。

SELECT f.location 
FROM Families f

当执行此查询时,它会生成以下输出。

[ 
   { 
      "location": { 
         "state": "NY", 
         "county": "Manhattan", 
         "city": "NY" 
      } 
   }, 
	
   { 
      "location": { 
         "state": "NY", 
         "county": "Queens", 
         "city": "Forest Hills" 
      } 
   },
	
   { 
      "location": { 
         "state": "WA", 
         "county": "King", 
         "city": "Seattle" 
      } 
   } 
]