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 |

|  | xiaobai  |     | english   |

|  | xiaobai  |     | physics   |

|  | xiaobai  |     | shuxue    |

|  | xiaohei  |     | astronaut |

|  | xiaohei  |     | shuxue    |

|  | xiaohei  |     | physics   |

|  | xiaohei  |     | english   |

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

 rows in set (0.00 sec)

mysql> select name,avg(score) from test group by name;

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

| name     | avg(score) |

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

| xiaobai  |    80.0000 |

| xiaohei  |    80.0000 |

| xiaohong |    82.2500 |

| xiaoming |    82.2500 |

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

 rows in set (0.01 sec)

mysql> select name,sum(score)/count(*) from test group by name;

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

| name     | sum(score)/count(*) |

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

| xiaobai  |             80.0000 |

| xiaohei  |             80.0000 |

| xiaohong |             82.2500 |

| xiaoming |             82.2500 |

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

 rows in set (0.00 sec)