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。

In relational databases, SQL aliases are used to temporarily rename a table or a column heading. Similarly, in DocumentDB, aliases are used to temporarily rename a JSON document, sub-document, object or any field.

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。

The renaming is a temporary change and the actual document does not change. Basically, aliases are created to make field/document names more readable. For aliasing, AS keyword is used which is optional.

我们从前一个例子中考虑三个类似的文档。

Let’s consider three similar documents from the ones used in previous examples.

以下是 AndersenFamily 文档。

Following is the AndersenFamily document.

{
   "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。

Following is the SmithFamily document.

{
   "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。

Following is the WakefieldFamily document.

{
   "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。

Let’s take a look at an example to discuss the aliases.

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。

Following is the query which will join the root to children subdocument. We have aliases such as f.id AS familyName, c.givenName AS childGivenName, and 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。

When the above query is executed, it produces the following output.

[
   {
      "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。

The above output shows that the filed names are changed, but it is a temporary change and the original documents are not modified.