mysql 获取字符串的长度

mysql> select * from test;
+----+------------+-------+-----------+
| id | name       | score | subject   |
+----+------------+-------+-----------+
|  1 | xiaoming   |    89 | shuxue    |
|  2 | xiaohong   |    89 | shuxue    |
|  3 | xiaohong   |    80 | english   |
|  4 | xiaohong   |    80 | physics   |
|  5 | xiaohong   |    80 | astronaut |
|  6 | xiaoming   |    80 | physics   |
|  7 | xiaoming   |    80 | astronaut |
|  8 | xiaoming   |    80 | english   |
|  9 | xiaobai    |    80 | astronaut |
| 10 | 1.2xiaobai |    80 | english   |
| 11 | 2.2xiaobai |    80 | physics   |
| 12 | 3xiaobai   |    80 | shuxue    |
| 13 | 123xiaohei |    80 | astronaut |
| 14 | xiaohei    |    80 | shuxue    |
| 15 | xiaohei    |    80 | physics   |
| 16 | .12xiaohei |    80 | english   |
+----+------------+-------+-----------+
16 rows in set (0.00 sec)

mysql> select length(name) from test where id=3;
+--------------+
| length(name) |
+--------------+
|            8 |
+--------------+
1 row in set (0.00 sec)