# 获取 JSON 数组的长度和大小
<a name="length-and-size"></a>

要获取 JSON 数组的长度和大小，可以使用 `json_array_length` 和 `json_size` 函数。

## 例如：`json_array_length`
<a name="example-json-array-length"></a>

要获取 JSON 编码数组的长度，请使用 `json_array_length` 函数。

```
WITH dataset AS (
  SELECT * FROM (VALUES
    (JSON '{"name":
            "Bob Smith",
            "org":
            "legal",
            "projects": [{"name":"project1", "completed":false}]}'),
    (JSON '{"name": "Susan Smith",
            "org": "engineering",
            "projects": [{"name":"project2", "completed":true},
                         {"name":"project3", "completed":true}]}'),
    (JSON '{"name": "Jane Smith",
             "org": "finance",
             "projects": [{"name":"project2", "completed":true}]}')
  ) AS t (users)
)
SELECT
  json_extract_scalar(users, '$.name') as name,
  json_array_length(json_extract(users, '$.projects')) as count
FROM dataset
ORDER BY count DESC
```

此查询返回以下结果：

```
+---------------------+
| name        | count |
+---------------------+
| Susan Smith | 2     |
+---------------------+
| Bob Smith   | 1     |
+---------------------+
| Jane Smith  | 1     |
+---------------------+
```

## 例如：`json_size`
<a name="example-json-size"></a>

要获取 JSON 编码的数组或对象的大小，请使用 `json_size` 函数，并指定将 JSON 字符串和 `JSONPath` 表达式包含到该数组或对象中的列。

```
WITH dataset AS (
  SELECT * FROM (VALUES
    (JSON '{"name": "Bob Smith", "org": "legal", "projects": [{"name":"project1", "completed":false}]}'),
    (JSON '{"name": "Susan Smith", "org": "engineering", "projects": [{"name":"project2", "completed":true},{"name":"project3", "completed":true}]}'),
    (JSON '{"name": "Jane Smith", "org": "finance", "projects": [{"name":"project2", "completed":true}]}')
  ) AS t (users)
)
SELECT
  json_extract_scalar(users, '$.name') as name,
  json_size(users, '$.projects') as count
FROM dataset
ORDER BY count DESC
```

此查询返回以下结果：

```
+---------------------+
| name        | count |
+---------------------+
| Susan Smith | 2     |
+---------------------+
| Bob Smith   | 1     |
+---------------------+
| Jane Smith  | 1     |
+---------------------+
```