Documentdb Sql 简明教程

DocumentDB SQL - Aliasing

在关系数据库中，SQL 别名用于临时重命名表或列标题。类似地，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，实际文档并不会更改。基本上，别名是为了使字段/文档名称更具可读性。对于别名，使用可选的 AS 关键字。

我们从前一个例子中考虑三个类似的文档。

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
}

我们来看看一个讨论别名的例子。

aliase

以下是将根与子文档连接的查询。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

执行以上查询后，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"
   }
]

上面的输出显示文件名称已更改，但这是临时更改，原始文档未修改。