ekuiper-new/docs/zh_CN/json_expr.md

样本数据

{
  "name": {"first": "Tom", "last": "Anderson"},
  "age":37,
  "children": ["Sara","Alex","Jack"],
  "fav.movie": "Deer Hunter",
  "friends": [
    {"first": "Dale", "last": "Murphy", "age": 44},
    {"first": "Roger", "last": "Craig", "age": 68},
    {"first": "Jane", "last": "Murphy", "age": 47}
  ],
    "followers": {
        "Group1": [
            {"first": "John", "last": "Shavor", "age": 22},
            {"first": "Ken", "last": "Miller", "age": 33}
        ],
        "Group2": [
            {"first": "Alice", "last": "Murphy", "age": 33},
            {"first": "Brian", "last": "Craig", "age": 44}
        ]
    }
   "ops": {
    "functionA": {"numArgs": 2},
    "functionB": {"numArgs": 3},
    "functionC": {"variadic": true}
  }
}

基本表达式

识别码

源引用（.）源解引用运算符可用于通过引用源流或表来指定列。'->引用选择嵌套JSON对象中的键。

SELECT demo.age FROM demo
{"age" : 37}

SELECT demo.name->first FROM demo
{"first" : "Tom"}

SELECT name->first AS fname FROM demo
{"fname": "Tom"}

索引表达式

索引表达式使您可以选择列表中的特定元素。 它看起来应该类似于普通编程语言中的数组访问。 索引基于0。

SELECT children FROM demo
{
    "children": ["Sara","Alex","Jack"]
}

SELECT children[0] FROM demo
{
    "children": "Sara"
}

SELECT d.friends[0]->last FROM demo AS d
{
    "last" : "Murphy"
}

切片

切片允许您选择数组的连续子集。

field[from:to] 如果未指定from，则表示从数组的第一个元素开始; 如果未指定to，则表示以数组的最后一个元素结尾。

SELECT children[0:1] FROM demo
{
    "children": ["Sara","Alex"]
}

SELECT children[:] FROM demo == SELECT children FROM demo
{
    "children": ["Sara","Alex","Jack"]
}

SELECT children[:1] FROM demo
{
    "children": ["Sara","Alex"]
}

SELECT followers->Group1[:1]->first FROM demo

{
    "first": ["John","Alice"]
}

映射

列表和切片映射

通配符表达式创建列表映射，它是JSON数组上的映射。

SELECT demo.friends[*]->first FROM demo
{
    "first": ["Dale", "Roger", "Jane"]
}

SELECT friends[:1]->first FROM demo
{
    "first": ["Dale", "Roger"]
}

对象映射

SELECT ops->*->numArgs FROM demo

{ "numArgs" : [2, 3] }