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;（查询id为3的name字符串长度）+--------------+| length(name) |+--------------+| 8 |+--------------+1 row in set (0.00 sec)