mysql> select * from test;

+----+------------+-------+-----------+

| id | name       | score | subject   |

+----+------------+-------+-----------+

|   | xiaoming   |     | shuxue    |

|   | xiaohong   |     | shuxue    |

|   | xiaohong   |     | english   |

|   | xiaohong   |     | physics   |

|   | xiaohong   |     | astronaut |

|   | xiaoming   |     | physics   |

|   | xiaoming   |     | astronaut |

|   | xiaoming   |     | english   |

|   | xiaobai    |     | astronaut |

|  | .2xiaobai |     | english   |

|  | .2xiaobai |     | physics   |

|  | 3xiaobai   |     | shuxue    |

|  | 123xiaohei |     | astronaut |

|  | xiaohei    |     | shuxue    |

|  | xiaohei    |     | physics   |

|  | .12xiaohei |     | english   |

+----+------------+-------+-----------+

 rows in set (0.00 sec)

mysql> select length(name) from test where id=;

+--------------+

| length(name) |

+--------------+

|             |

+--------------+

 row in set (0.00 sec)