# **JSON_EXTRACT_FLOAT64()**

## **Function Description**

`JSON_EXTRACT_FLOAT64()` The value used to extract the value of the specified path from JSON data.

If you compare in where conditions:

- If type is json object comparison, use [JSON EXTRACT()](json_extract.md);
- If the type is a string type, use [JSON_EXTRACT_STRING()](json_extract_string.md);
- If type is float or int, use `JSON_EXTRACT_FLOAT64()`.

## **Grammar Structure**

```sql
select col_name from tab_name where json_extract_float64(jsonDoc, pathExpression)= number;
```

## **Parameter definition**

| Parameters | Description |
| ---- | ---- |
| jsonDoc | This is a column or expression containing JSON data. |
| pathExpression | Indicates the path to access a value in a JSON document. Only one path can be received at a time. The path starts with `$`, representing the root of the JSON document, followed by the dot number `.` and key name or access elements of the array with square brackets [ ]. |
| number | Specifies the value to be extracted in JSON data, which is a numerical type. |

The path expression must start with the `$` character:

- `,` followed by a key name, name the members in the object with the given key. Key names need to be included in double quotes.

- `[N]`: After selecting *path* of the array, name the value at position `N` in the array. The array position is an integer starting from zero. If the array is negative, an error will be reported.

- The path can contain `*` or `**` wildcard:

   + `.[*]` calculates the values of all members in the JSON object.

   + `[*]` calculates the values of all elements in the JSON array.

   + `prefix**suffix`: Calculates all paths that start with a named prefix and end with a named suffix.

- Paths (or data that do not exist) in the document are evaluated as `NULL`.

## **Example**

```text
create table student(n1 int,n2 json);
insert into student values
    (1,'{"name": "tom", "age": 18, "score": 90,"gender": "male"}'),
    (2,'{"name": "bob", "age": 20, "score": 80,"gender": "male"}'),
    (3,'{"name": "jane", "age": 17, "score": 95,"gender": "female"}'),
    (4,'{"name": "lily", "age": 19, "score": 79,"gender": "female"}');

mysql> select n1 from student where json_extract_float64(n2,'$.age')=19;
+------+
| n1 |
+------+
| 4 |
+------+
1 row in set (0.00 sec)

select json_extract_float64(n2,'$.age')=19;
```