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Linux第11周

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不飞则已，一飞冲天；不鸣则已，一鸣惊人。这篇文章主要讲述Linux第11周相关的知识，希望能为你提供帮助。
【Linux第11周】1、 导入hellodb.sql生成数据库

[root@centos8-2 ~]# yum -y install mysql-server
[root@centos8-2 ~]# systemctl enable --now mysqld
[root@centos8-2 ~]# rz -E
rz waiting to receive.
[root@centos8-2 ~]# mysql
mysql> source hellodb_innodb.sql

mysql> show databases;
+--------------------+
| Database|
+--------------------+
| hellodb|
| information_schema |
| mysql|
| performance_schema |
| sys|
+--------------------+

(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
mysql> use hellodb;
Database changed
mysql> show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes|
| coc|
| courses|
| scores|
| students|
| teachers|
| toc|
+-------------------+
7 rows in set (0.00 sec)
mysql> select *from students;
mysql> 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 |
+--------------+-----+

(2) 以ClassID为分组依据，显示每组的平均年龄
mysql> select classid,avg(age) from students group by classid order by classid ASC;
+---------+----------+
| 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
mysql> select classid,avg(age) from students group by classid having avg(age) > 30 order by classid ASC;
+---------+----------+
| classid | avg(age) |
+---------+----------+
|NULL |63.5000 |
|2 |36.0000 |
|5 |46.0000 |
+---------+----------+
3 rows in set (0.00 sec)

(4) 显示以L开头的名字的同学的信息
mysql> 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 |
+-------+-------------+-----+--------+---------+------

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