1、 导入hellodb.sql生成数据库
[root@c7-37-103-mini ~]# mysql < /data/app/hellodb_innodb.sql
[root@c7-37-103-mini ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 7
Server version: 5.5.65-MariaDB MariaDB Server
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| hellodb |
| mysql |
| performance_schema |
| test |
+--------------------+
5 rows in set (0.00 sec)
MariaDB [(none)]> use hellodb;
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
MariaDB [hellodb]> select * from students;
+-------+---------------+-----+--------+---------+-----------+
| 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 |
| 6 | Shi Qing | 46 | M | 5 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 9 | Ren Yingying | 20 | F | 6 | NULL |
| 10 | Yue Lingshan | 19 | F | 3 | NULL |
| 11 | Yuan Chengzhi | 23 | M | 6 | NULL |
| 12 | Wen Qingqing | 19 | F | 1 | NULL |
| 13 | Tian Boguang | 33 | M | 2 | NULL |
| 14 | Lu Wushuang | 17 | F | 3 | NULL |
| 15 | Duan Yu | 19 | M | 4 | NULL |
| 16 | Xu Zhu | 21 | M | 1 | NULL |
| 17 | Lin Chong | 25 | M | 4 | NULL |
| 18 | Hua Rong | 23 | M | 7 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 20 | Diao Chan | 19 | F | 7 | NULL |
| 21 | Huang Yueying | 22 | F | 6 | NULL |
| 22 | Xiao Qiao | 20 | F | 1 | NULL |
| 23 | Ma Chao | 23 | M | 4 | NULL |
| 24 | Xu Xian | 27 | M | NULL | NULL |
| 25 | Sun Dasheng | 100 | M | NULL | NULL |
+-------+---------------+-----+--------+---------+-----------+
25 rows in set (0.01 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 ;
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 (0.07 sec)
(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 |
+---------+----------+
8 rows in set (0.04 sec)
#有空值需要排除
MariaDB [hellodb]> select ClassID,avg(age) from students where classid is not null group by classid ;
+---------+----------+
| 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 (0.01 sec)
(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 where classid is not null and age >30 group by classid ;
+---------+----------+
| ClassID | avg(age) |
+---------+----------+
| 2 | 43.0000 |
| 4 | 32.0000 |
| 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;
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)
2、数据库授权magedu用户，允许192.168.1.0/24网段可以连接mysql
方法1：先创建用户，然后授权
create user 'magedu'@'192.168.1.%' identified by 'centos';
#创建用户还需要授权用户可以管理的数据库,hellodb.*表示可以管理hellodb的所有资源
grant all on hellodb.* to magedu;
方法2: 方法2：授权时直接创建用户
grant all on hellodb.* to 'magedu'@'192.168.1.%' identified by 'centos';
3、总结mysql常见的存储引擎以及特点。
MySQL数据库常用的存储引擎MyISAM 和InnoDB，MySQL5.5以后其默认存储引擎为InnoDB，相当于MyISAM淘汰了；他们各自的特点如下：
MyISAM引擎特点
不支持事务
表级锁定
读写相互阻塞，写入不能读，读时不能写
只缓存索引
不支持外键约束
不支持聚簇索引
读取数据较快，占用资源较少
不支持MVCC（多版本并发控制机制）高并发
崩溃恢复性较差
MySQL5.5.5前默认的数据库引擎
MyISAM存储引擎适用场景
只读（或者写较少）、表较小（可以接受长时间进行修复操作）
MyISAM引擎文件
其数据库目录下包含三个文件
tbl_name.frm 表格式定义
tbl_name.MYD 数据文件
tbl_name.MYI 索引文件
InnoDB引擎特点
行级锁
支持事务，适合处理大量短期事务
读写阻塞与事务隔离级别相关
可缓存数据和索引
支持聚簇索引
崩溃恢复性更好
支持MVCC高并发
从MySQL5.5后支持全文索引
从MySQL5.5.5开始为默认的数据库引擎
InnoDB数据库文件
所有InnoDB表的数据和索引放置于同一个表空间中
表空间文件：datadir定义的目录下
数据文件：ibddata1, ibddata2, ...
可以设置每个表单独使用一个表空间存储表的数据和索引
启用：innodb_file_per_table=ON
两类文件放在数据库独立目录中
数据文件(存储数据和索引)：tb_name.ibd
表格式定义：tb_name.frm
