---
{
    "title": "get_json_double",
    "language": "zh-CN"
}
---

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# get_json_double
## description
### Syntax

`DOUBLE get_json_double(VARCHAR json_str, VARCHAR json_path)`


解析并获取 json 字符串内指定路径的浮点型内容。
其中 json_path 必须以 $ 符号作为开头，使用 . 作为路径分割符。如果路径中包含 . ，则可以使用双引号包围。
使用 [ ] 表示数组下标，从 0 开始。
path 的内容不能包含 ", [ 和 ]。
如果 json_string 格式不对，或 json_path 格式不对，或无法找到匹配项，则返回 NULL。

## example

1. 获取 key 为 "k1" 的 value

```
mysql> SELECT get_json_double('{"k1":1.3, "k2":"2"}', "$.k1");
+-------------------------------------------------+
| get_json_double('{"k1":1.3, "k2":"2"}', '$.k1') |
+-------------------------------------------------+
|                                             1.3 |
+-------------------------------------------------+
```

2. 获取 key 为 "my.key" 的数组中第二个元素

```
mysql> SELECT get_json_double('{"k1":"v1", "my.key":[1.1, 2.2, 3.3]}', '$."my.key"[1]');
+---------------------------------------------------------------------------+
| get_json_double('{"k1":"v1", "my.key":[1.1, 2.2, 3.3]}', '$."my.key"[1]') |
+---------------------------------------------------------------------------+
|                                                                       2.2 |
+---------------------------------------------------------------------------+
```

3. 获取二级路径为 k1.key -> k2 的数组中，第一个元素
```
mysql> SELECT get_json_double('{"k1.key":{"k2":[1.1, 2.2]}}', '$."k1.key".k2[0]');
+---------------------------------------------------------------------+
| get_json_double('{"k1.key":{"k2":[1.1, 2.2]}}', '$."k1.key".k2[0]') |
+---------------------------------------------------------------------+
|                                                                 1.1 |
+---------------------------------------------------------------------+
```
## keyword
GET_JSON_DOUBLE,GET,JSON,DOUBLE