mysql练习

Posted 2022-03-17 落阳٩

导入hellodb.sql生成数据库

#准备环境
[root@centos8 ~]# mysql < hellodb_innodb.sql 
[root@centos8 ~]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \\g.
Your MySQL connection id is 10
Server version: 8.0.26 Source distribution

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type help; or \\h for help. Type \\c to clear the current input statement.

mysql> show databases;     #查看数据库
+--------------------+
| Database           |
+--------------------+
| hellodb            |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)
mysql> use hellodb;  #进入hellodb数据库
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;  #查看hellodb中的表
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.00 sec)
（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> 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 (0.00 sec)

(2) 以ClassID为分组依据，显示每组的平均年龄####### 
#一旦分组 group by ，select语句后只跟分组的字段，聚合函数
mysql> select classid,avg(age) from students group by classid;
+---------+----------+
| classid | avg(age) |
+---------+----------+
|       2 |  36.0000 |
|       1 |  20.5000 |
|       4 |  24.7500 |
|       3 |  20.2500 |
|       5 |  46.0000 |
|       7 |  19.6667 |
|       6 |  20.7500 |
|    NULL |  63.5000 |
+---------+----------+
8 rows in set (0.00 sec)
(3) 显示第2题中平均年龄大于30的分组及平均年龄####### 
##HAVING: 对分组聚合运算后的结果指定过滤条件
mysql> select classid,avg(age) avg from students group by classid having avg>30;
+---------+---------+
| classid | avg     |
+---------+---------+
|       2 | 36.0000 |
|       5 | 46.0000 |
|    NULL | 63.5000 |
+---------+---------+
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 |
+-------+-------------+-----+--------+---------+-----------+
3 rows in set (0.00 sec)

数据库授权magedu用户，允许192.168.1.0/24网段可以连接mysql

#mysql在8.0之后取消了常见用户同时授权的操作
mysql> create user magedu@192.168.1.% identified by 123456;
Query OK, 0 rows affected (0.04 sec)
mysql> select user,host from mysql.user;
+------------------+-------------+
| user             | host        |
+------------------+-------------+
| magedu           | 192.168.1.% |
| mysql.infoschema | localhost   |
| mysql.session    | localhost   |
| mysql.sys        | localhost   |
| root             | localhost   |
+------------------+-------------+
5 rows in set (0.00 sec)
mysql> grant all on *.* to magedu@192.168.1.%;  #授权账号
Query OK, 0 rows affected (0.01 sec)