马哥Linux第十四周

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 stuid,name,avg(age),gender,classid,teacherid from students group by classid;
+-------+--------------+----------+--------+---------+-----------+
| stuid | name         | avg(age) | gender | classid | teacherid |
+-------+--------------+----------+--------+---------+-----------+
|    24 | Xu Xian      |  63.5000 | M      |    NULL |      NULL |
|     2 | Shi Potian   |  20.5000 | M      |       1 |         7 |
|     1 | Shi Zhongyu  |  36.0000 | M      |       2 |         3 |
|     5 | Yu Yutong    |  20.2500 | M      |       3 |         1 |
|     4 | Ding Dian    |  24.7500 | M      |       4 |         4 |
|     6 | Shi Qing     |  46.0000 | M      |       5 |      NULL |
|     9 | Ren Yingying |  20.7500 | F      |       6 |      NULL |
|     8 | Lin Daiyu    |  19.6667 | F      |       7 |      NULL |
+-------+--------------+----------+--------+---------+-----------+
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

MariaDB [hellodb]> select avg(age),classid from students group by classid having avg(age) > 30;
+----------+---------+
| avg(age) | classid |
+----------+---------+
|  63.5000 |    NULL |
|  36.0000 |       2 |
|  46.0000 |       5 |
+----------+---------+
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

#授权magedu
MariaDB [(none)]> grant all on *.* to magedu@'192.168.1.%' identified by '123456';
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)

#验证
[root@ka2 ~]# mysql -umagedu -p123456 -h192.168.1.177
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.60-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 |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.02 sec)

MariaDB [(none)]> select host,user,password from mysql.user;
+--------------+--------+-------------------------------------------+
| host         | user   | password                                  |
+--------------+--------+-------------------------------------------+
| localhost    | root   |                                           |
| centos7.6    | root   |                                           |
| 127.0.0.1    | root   |                                           |
| ::1          | root   |                                           |
| 192.168.1.%  | magedu | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+--------------+--------+-------------------------------------------+

3、总结mysql常见的存储引擎以及特点。

• **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

• 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