马哥博客作业第十三周

1、如何将 hellodb_innodb.sql导入到数据库中

[root@localhost ~]#mysql < hellodb_innodb.sql

2、在学生表中，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 as 姓名,age as 年龄 from students where age > 25 and gender='m';
+--------------+--------+
| 姓名         | 年龄   | 
+--------------+--------+
| Xie Yanke    |     53 | 
| Ding Dian    |     32 | 
| Yu Yutong    |     26 | 
| Shi Qing     |     46 | 
| Tian Boguang |     33 | 
| Xu Xian      |     27 | 
| Sun Dasheng  |    100 |
+--------------+--------+
7 rows in set (0.00 sec)

3、在学生表中，以ClassID为分组依据，查询显示每组的平均年龄

MariaDB [hellodb]> select classid,avg(age) as 平均年龄 from students  group by classid;
+---------+--------------+
| classid | 平均年龄     |
+---------+--------------+
|    NULL |      63.5000 |
|       1 |      20.5000 |
|       2 |      36.0000 |
|       3 |      20.2500 |
|       4 |      24.7500 |
|       5 |      46.0000 |
|       6 |      20.7500 |
|       7 |      19.6667 |
+---------+--------------+
8 rows in set (0.00 sec)

4、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) as 平均年龄 from (select * from students where age > 25 and gender='m') as t1 group by classid having avg(age)>30 ;
+---------+--------------+
| ClassID | 平均年龄     |
+---------+--------------+
|    NULL |      63.5000 |
|       2 |      43.0000 |
|       4 |      32.0000 |
|       5 |      46.0000 |
+---------+--------------+
4 rows in set (0.00 sec)

5、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 |
+-------+-------------+-----+--------+---------+-----------+
3 rows in set (0.00 sec)

6、显示老师ID非空的同学的相关信息

MariaDB [hellodb]> select * from students where teacherid is not null;
+-------+-------------+-----+--------+---------+-----------+
| StuID | Name        | Age | Gender | ClassID | TeacherID |
+-------+-------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu |  22 | M      |       2 |         3 |
|     2 | Shi Potian  |  22 | M      |       1 |         7 |
|     3 | Xie Yanke   |  53 | M      |       2 |        16 |
|     4 | Ding Dian   |  32 | M      |       4 |         4 |
|     5 | Yu Yutong   |  26 | M      |       3 |         1 |
+-------+-------------+-----+--------+---------+-----------+
5 rows in set (0.00 sec)

7、students表中，查询以年龄排序后的数据，并且显示年龄最大的前10位同学的信息

MariaDB [hellodb]> select * from students order by age desc limit 10;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|    25 | Sun Dasheng  | 100 | M      |    NULL |      NULL |
|     3 | Xie Yanke    |  53 | M      |       2 |        16 |
|     6 | Shi Qing     |  46 | M      |       5 |      NULL |
|    13 | Tian Boguang |  33 | M      |       2 |      NULL |
|     4 | Ding Dian    |  32 | M      |       4 |         4 |
|    24 | Xu Xian      |  27 | M      |    NULL |      NULL |
|     5 | Yu Yutong    |  26 | M      |       3 |         1 |
|    17 | Lin Chong    |  25 | M      |       4 |      NULL |
|    18 | Hua Rong     |  23 | M      |       7 |      NULL |
|    23 | Ma Chao      |  23 | M      |       4 |      NULL |
+-------+--------------+-----+--------+---------+-----------+
10 rows in set (0.00 sec)

8、students表中，查询年龄大于等于20岁，小于等于25岁的同学的信息

MariaDB [hellodb]> select * from students where age >= 20 and age <= 25;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name          | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  22 | M      |       1 |         7 |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL |
+-------+---------------+-----+--------+---------+-----------+
10 rows in set (0.00 sec)

9、以ClassID分组，显示每班的同学的人数

MariaDB [hellodb]> select classid,count(stuid) as 总人数 from students where classid is not null group by classid;
+---------+-----------+
| classid | 总人数    |
+---------+-----------+
|       1 |         4 |
|       2 |         3 |
|       3 |         4 |
|       4 |         4 |
|       5 |         1 |
|       6 |         4 |
|       7 |         3 |
+---------+-----------+
7 rows in set (0.00 sec)

10、以ClassID分组，显示其平均年龄大于25的班级

MariaDB [hellodb]> select classid,avg(age) as 平均年龄 from students where classid is not null group by classid having 平均年龄 > 25;
+---------+--------------+
| classid | 平均年龄     |
+---------+--------------+
|       2 |      36.0000 |
|       5 |      46.0000 |
+---------+--------------+
2 rows in set (0.00 sec)