MySQL数据库基础操作

1、 导入hellodb.sql生成数据库

[root@centos7 ~]# mysql < hellodb_innodb.sql 

(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 * from students where Age >25 and Gender='M';
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     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 |
|    13 | Tian Boguang |  33 | M      |       2 |      NULL |
|    24 | Xu Xian      |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng  | 100 | M      |    NULL |      NULL |
+-------+--------------+-----+--------+---------+-----------+

(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 |
+---------+----------+

(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 group by ClassID having avg(Age) >30;
+---------+----------+
| ClassID | avg(Age) |
+---------+----------+
|    NULL |  63.5000 |
|       2 |  36.0000 |
|       5 |  46.0000 |
+---------+----------+

(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 |
+-------+-------------+-----+--------+---------+-----------+

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

MariaDB [mysql]> create user magedu@'192.168.1.%' IDENTIFIED BY '123456';

MariaDB [(none)]> SHOW GRANTS FOR magedu@'192.168.1.%';
+-----------------------------------------------------------------------------------------------------------------+
| Grants for magedu@192.168.1.%                                                                                   |
+-----------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'magedu'@'192.168.1.%' IDENTIFIED BY PASSWORD '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9' |
+-----------------------------------------------------------------------------------------------------------------+