导入hellodb.sql生成数据库

MariaDB [mysql]> source /root/hellodb_innodb.sql

(1) 在students表中，查询年龄大于25岁，且为男性的同学的名字和年龄 

MariaDB [hellodb]> select Name,Gender,Age from students where Age>25 and Gender='M';
+--------------+--------+-----+
| Name         | Gender | Age |
+--------------+--------+-----+
| Xie Yanke    | M      |  53 |
| Ding Dian    | M      |  32 |
| Yu Yutong    | M      |  26 |
| Shi Qing     | M      |  46 |
| Tian Boguang | M      |  33 |
| Xu Xian      | M      |  27 |
| Sun Dasheng  | M      | 100 |
+--------------+--------+-----+

(2) 以ClassID为分组依据，显示每组的平均年龄

MariaDB [hellodb]> select ClassID,avg(age) from students group by ClassID;
+---------+----------+
| ClassID | avg(age) |
+---------+----------+
|    NULL |  63.5000 |
|       1 |  20.5000 |
|       2 |  36.0000 |
|       3 |  20.2500 |
|       4 |  24.7500 |
|       5 |  46.0000 |
|       6 |  20.7500 |
|       7 |  19.6667 |
+---------+----------+

(3) 显示第2题中平均年龄大于30的分组及平均年龄

MariaDB [hellodb]> select ClassID,avg(age) from students group by ClassID having avg(age)>30;
+---------+----------+
| ClassID | avg(age) |
+---------+----------+
|    NULL |  63.5000 |
|       2 |  36.0000 |
|       5 |  46.0000 |
+---------+----------+

(4) 显示以L开头的名字的同学的信息

MariaDB [hellodb]> select * from students where name like 'L%';
+-------+-------------+-----+--------+---------+-----------+
| StuID | Name        | Age | Gender | ClassID | TeacherID |
+-------+-------------+-----+--------+---------+-----------+
|     8 | Lin Daiyu   |  17 | F      |       7 |      NULL |
|    14 | Lu Wushuang |  17 | F      |       3 |      NULL |
|    17 | Lin Chong   |  25 | M      |       4 |      NULL |
+-------+-------------+-----+--------+---------+-----------+