1、导入hellodb.sql生成数据库
(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 (0.00 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 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 (0.00 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 s.classid,s.aage from (select classid,avg(age) as aage from students where classid is not null group by classid) as s where s.aage > 30;
+---------+---------+
| classid | aage |
+---------+---------+
| 2 | 36.0000 |
| 5 | 46.0000 |
+---------+---------+
2 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
(1)数据库服务器设置
[root@centos01 ~]#mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 3
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)]> grant all on *.* to 'magedu'@'192.168.7.%' identified by '123123';
Query OK, 0 rows affected (0.00 sec)
(2)客户端连接
[root@centos02 ~]#mysql -umagedu -h192.168.7.71 -p123123
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 4
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)]>
3、总结mysql常见的存储引擎以及特点
常见存储引擎有MyISAM,InnoDB,Memory,Archive,NDB等
MyISAM
(1)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
(2)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）
(3)引擎文件
tbl_name.frm 表格式定义
tbl_name.MYD 数据文件
tbl_name.MYI 索引文件
InnoDB
(1)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
(2)引擎文件
所有InnoDB表的数据和索引放置于同一个表空间中
每个表单独使用一个表空间存储表的数据和索引