第十三周作业

1、如何将 hellodb_innodb.sql导入到数据库中

 答：

方法1：在命令行中

 

[root@centos8 ~]#mysql < hellodb_innodb.sql 

 

方法2：在数据库中

MariaDB [(none)]> source 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

 答：

MariaDB [hellodb]> SELECT name,age FROM students WHERE age > 25 AND gender='M';
+--------------+-----+
| name         | age |
+--------------+-----+
| 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 (0.000 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

 答：

MariaDB [hellodb]> SELECT classid,avg(age) FROM students GROUP BY classid HAVING classid IS NOT NULL;
+---------+----------+
| classid | avg(age) |
+---------+----------+
|       1 |  20.5000 |
|       2 |  36.0000 |
|       3 |  20.2500 |
|       4 |  24.7500 |
|       5 |  46.0000 |
|       6 |  20.7500 |
|       7 |  19.6667 |
+---------+----------+
7 rows in set (0.000 sec)

 

 

4、显示第3题中平均年龄大于30的分组及平均年龄

 答：

MariaDB [hellodb]> SELECT classid,avg(age) FROM students GROUP BY classid HAVING classid IS NOT NULL AND avg(age) > 30;
+---------+----------+
| classid | avg(age) |
+---------+----------+
|       2 |  36.0000 |
|       5 |  46.0000 |
+---------+----------+
2 rows in set (0.001 sec)

 

 

5、显示以L开头的名字的同学的信息

 答：

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 (0.000 sec)

 

 

6、显示老师ID非空的同学的相关信息

 答：

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 (0.000 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

 答：

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 |
|    23 | Ma Chao      |  23 | M      |       4 |      NULL |
|    18 | Hua Rong     |  23 | M      |       7 |      NULL |
+-------+--------------+-----+--------+---------+-----------+
10 rows in set (0.000 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

 答：

MariaDB [hellodb]> SELECT * FROM students WHERE age BETWEEN 20 AND 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 (0.000 sec)

 

 

9、以ClassID分组，显示每班的同学的人数

 答：

MariaDB [hellodb]> SELECT classid,count(name) '每班人数' FROM students GROUP BY classid HAVING classid IS NOT NULL;
+---------+--------------+
| classid | 每班人数     |
+---------+--------------+
|       1 |            4 |
|       2 |            3 |
|       3 |            4 |
|       4 |            4 |
|       5 |            1 |
|       6 |            4 |
|       7 |            3 |
+---------+--------------+
7 rows in set (0.000 sec)

 

10、以ClassID分组，显示其平均年龄大于25的班级

答：

MariaDB [hellodb]> SELECT classid,avg(age) '平均年龄' FROM students WHERE classid IS NOT NULL GROUP BY classid HAVING avg(age)>25;
+---------+--------------+
| classid | 平均年龄     |
+---------+--------------+
|       2 |      36.0000 |
|       5 |      46.0000 |
+---------+--------------+
2 rows in set (0.000 sec)