SQL VALUE
当您知道您只返回一个值时，VALUE 关键字可以通过避免创建完整对象的开销来帮助生成更精简的结果集。 VALUE 关键字提供了一种返回 JSON 值的方法。
我们来看一个简单的例子。
以下是带有 VALUE 关键字的查询。
SELECT VALUE "Hello World, this is DocumentDB SQL Tutorial"
当这个查询被执行时，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，让我们考虑前面示例中的三个文档。
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
当这个查询被执行时，它返回没有位置标签的返回地址。
[
{
"state": "NY",
"county": "Manhattan",
"city": "NY"
},
{
"state": "NY",
"county": "Queens",
"city": "Forest Hills"
},
{
"state": "WA",
"county": "King",
"city": "Seattle"
}
]
如果我们现在在没有 VALUE 关键字的情况下指定相同的查询，那么它将返回带有位置标签的地址。以下是查询。
SELECT f.location
FROM Families f
执行此查询时，会产生以下输出。
[
{
"location": {
"state": "NY",
"county": "Manhattan",
"city": "NY"
}
},
{
"location": {
"state": "NY",
"county": "Queens",
"city": "Forest Hills"
}
},
{
"location": {
"state": "WA",
"county": "King",
"city": "Seattle"
}
}
]
