# 确定字符串长度

__*LENGTH 函数*__
__*CHAR_LENGTH 函数*__

+ `LENGTH()`: 以字节为单位返回字符串长度
+ `CHAR_LENGTH()`: 返回字符串长度（以字符为单位）
+ 例如:
  + `select length('TiDB 部署中'), char_length('TiDB 部署中');` 
```
tidb> SELECT length('TiDB 部署中'), char_length('TiDB 部署中');
+--------------------------+-------------------------------+
| length('~!@TiDB 部署中@!~')     | char_length('TiDB 部署中')     |
+--------------------------+-------------------------------+
|                       ~!@14@!~ |                             8 |
+--------------------------+-------------------------------+
1 row in set (0.01 sec)
```
--------------------------------------------------------------------
默认字符集显然不是 ASCII:
```
tidb> SELECT length('TiDB 部署中'), char_length('TiDB 部署中'), length(convert('TiDB 部署中' using ascii));
+--------------------------+-------------------------------+-----------------------------------------------+
| length('TiDB 部署中')    | char_length('TiDB 部署中')    | length(convert('TiDB 部署中' using ascii))    |
+--------------------------+-------------------------------+-----------------------------------------------+
| 14                       | 8                             | 23                                            |
+--------------------------+-------------------------------+-----------------------------------------------+
1 row in set (0.00 sec)
```

- LENGTH()	返回字符串长度,单位为字节
- CHAR_LENGTH()	返回字符串的字符长度