Linux下MySQL的简单使用（二）

上一篇我们介绍到一些Linux的简单命令的使用，今天我们更深入了解一下MySQL！

一.多表查询

这篇通过实例来讲述多表查询，目的是穷尽所有的场景和所有的方法，并且对每个方法的使用做实例。 首先先列举本篇用到的分类(内连接，外连接，交叉连接)和连接方法：

A）内连接：join，inner join

B）外连接：left join，left outer join，right join，right outer join，union

C）交叉连接：cross join

首先导入hellodb.sql，以下的操作都是基于此：

1.内连接：仅查看有老师的学员和有学员的老师的信息

mysql> select s.name student_name,t.name teacher_name from students s inner join teachers t on s.teacherid=t.tid;+----------------+---------------+
| student_name   | teacher_name  |
+----------------+---------------+
| Sun Shangxiang | Liu Bang      |
| Hou Yi         | Wu Zetian     |
| Da Ji          | Cheng Jisihan |
+----------------+---------------+
3 rows in set (0.67 sec)

2.左内连接：显示所有学员信息，包含有老师的学员和没老师的学员

mysql> select s.name student_name,t.name teacher_name from students s left join teachers t on s.teacherid=t.tid;
+----------------+---------------+
| student_name   | teacher_name  |
+----------------+---------------+
| Hou Yi         | Wu Zetian     |
| Ya Se          | NULL          |
| An Qila        | NULL          |
| Da Ji          | Cheng Jisihan |
| Sun Shangxiang | Liu Bang      |
| Huang Zhong    | NULL          |
| Liu Bei        | NULL          |
| Guan Yu        | NULL          |
| Zhang Fei      | NULL          |
| Di Renjie      | NULL          |
| Li Yuanfang    | NULL          |
| Lan Lingwang   | NULL          |
| Wang Zhaojun   | NULL          |
| Bai Qi         | NULL          |
| A Ke           | NULL          |
| Cai Wenji      | NULL          |
| Lv Bu          | NULL          |
| Diao Chan      | NULL          |
| Gong Sunli     | NULL          |
| Ming Shiyin    | NULL          |
| Dun Shan       | NULL          |
| Zhou Yu        | NULL          |
| Mi Yue         | NULL          |
| Kai            | NULL          |
| Sun Wukong     | NULL          |
+----------------+---------------+
25 rows in set (0.05 sec)

3.右内连接：显示所有的老师信息，包含有学员的老师，和没学员的老师

mysql> select s.name student_name,t.name teacher_name from students s right join teachers t on s.teacherid=t.tid;

+----------------+---------------+
| student_name   | teacher_name  |
+----------------+---------------+
| Sun Shangxiang | Liu Bang      |
| NULL           | Ying Zheng    |
| Hou Yi         | Wu Zetian     |
| Da Ji          | Cheng Jisihan |
+----------------+---------------+
4 rows in set (0.00 sec)

4.左外连接：仅显示没老师的学员

select s.name student_name,t.name teacher_name from students s left join teachers t on s.teacherid=t.tid where t.name is null;
+--------------+--------------+
| student_name | teacher_name |
+--------------+--------------+
| Ya Se        | NULL         |
| An Qila      | NULL         |
| Huang Zhong  | NULL         |
| Liu Bei      | NULL         |
| Guan Yu      | NULL         |
| Zhang Fei    | NULL         |
| Di Renjie    | NULL         |
| Li Yuanfang  | NULL         |
| Lan Lingwang | NULL         |
| Wang Zhaojun | NULL         |
| Bai Qi       | NULL         |
| A Ke         | NULL         |
| Cai Wenji    | NULL         |
| Lv Bu        | NULL         |
| Diao Chan    | NULL         |
| Gong Sunli   | NULL         |
| Ming Shiyin  | NULL         |
| Dun Shan     | NULL         |
| Zhou Yu      | NULL         |
| Mi Yue       | NULL         |
| Kai          | NULL         |
| Sun Wukong   | NULL         |
+--------------+--------------+
22 rows in set (0.00 sec)

5.右外连接：仅显示没学员的老师

select s.name student_name,t.name teacher_name from students s right join teachers t on s.teacherid=t.tid where s.name is null;
+--------------+--------------+
| student_name | teacher_name |
+--------------+--------------+
| NULL         | Ying Zheng   |
+--------------+--------------+
1 row in set (0.00 sec)

6.并集：显示所有的老师和学员

mysql>  select s.name student_name,t.name teacher_name from students s left join teachers t on s.teacherid=t.tid
    -> union
    -> select s.name student_name,t.name teacher_name from students s right join teachers t on s.teacherid=t.tid;+----------------+---------------+
| student_name   | teacher_name  |
+----------------+---------------+
| Hou Yi         | Wu Zetian     |
| Ya Se          | NULL          |
| An Qila        | NULL          |
| Da Ji          | Cheng Jisihan |
| Sun Shangxiang | Liu Bang      |
| Huang Zhong    | NULL          |
| Liu Bei        | NULL          |
| Guan Yu        | NULL          |
| Zhang Fei      | NULL          |
| Di Renjie      | NULL          |
| Li Yuanfang    | NULL          |
| Lan Lingwang   | NULL          |
| Wang Zhaojun   | NULL          |
| Bai Qi         | NULL          |
| A Ke           | NULL          |
| Cai Wenji      | NULL          |
| Lv Bu          | NULL          |
| Diao Chan      | NULL          |
| Gong Sunli     | NULL          |
| Ming Shiyin    | NULL          |
| Dun Shan       | NULL          |
| Zhou Yu        | NULL          |
| Mi Yue         | NULL          |
| Kai            | NULL          |
| Sun Wukong     | NULL          |
| NULL           | Ying Zheng    |
+----------------+---------------+
26 rows in set (0.00 sec)

二.视图

视图是一种虚拟存在的表，视图可以理解为是一个容器，表通过条件查询之后，将查询后的结果放入这个容器内，然后给容器命名后即为视图。

视图相对于表的优势:

1.简单：使用视图的用户不必关系后面的表，只需要使用过滤好的内容就行了；

2.安全：因为对表的全新不能限制到表的行或者是列，所以可以通过视图来限制用户对表的访问权限；

3.数据独立：确定了视图的结构之后，如果给原来的表增加了列，并不会影响视图，增加行，视图的相对于的行也会增加，如果源表的列名称发生了改变，可以通过修改视图来解决。

 例：如下图在单表上创建视图，选择表的name，age列作为视图v1_student的列。

mysql> desc students;
+-----------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+----------------+
| StuID | int(10) unsigned | NO | PRI | NULL | auto_increment |
| Name | varchar(50) | NO | | NULL | |
| Age | tinyint(3) unsigned | NO | | NULL | |
| Gender | enum(‘F‘,‘M‘) | NO | | NULL | |
| ClassID | tinyint(3) unsigned | YES | | NULL | |
| TeacherID | int(10) unsigned | YES | | NULL | |
+-----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

mysql> create view v1_students as select name,age from students;
Query OK, 0 rows affected (0.00 sec)

查看已创建的视图

mysql> show create view v1_students\G;
*************************** 1. row ***************************
                View: v1_students
         Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1_students` AS select `students`.`Name` AS `name`,`students`.`Age` AS `age` from `students`
character_set_client: latin1
collation_connection: latin1_swedish_ci
1 row in set (0.00 sec)

删除已创建的视图

mysql> drop view v1_students;
Query OK, 0 rows affected (0.00 sec)

mysql>  select * from information_schema.views\G;
Empty set (0.06 sec)

三.函数

函数分为系统函数和自定义函数

系统函数：https://dev.mysql.com/doc/refman/5.7/en/func-op-summary ref.html，在这个官方的MySQL网站中，可以查看所有的系统函数。

自定义函数：(user-defined function UDF），保存在mysql.proc表中

1.创建一个自定义函数：

mysql> CREATE FUNCTION simpleFun() RETURNS VARCHAR(20) RETURN "Hello World!";
Query OK, 0 rows affected (0.05 sec)

mysql> select simplefun();
+--------------+
| simplefun()  |
+--------------+
| Hello World! |
+--------------+
1 row in set (0.05 sec)

2.查看所有的函数列表

mysql> show function status;
+---------+-----------+----------+----------------+---------------------+---------------------+---------------+---------+----------------------+----------------------+--------------------+
| Db      | Name      | Type     | Definer        | Modified            | Created             | Security_type | Comment | character_set_client | collation_connection | Database Collation |
+---------+-----------+----------+----------------+---------------------+---------------------+---------------+---------+----------------------+----------------------+--------------------+
| hellodb | simpleFun | FUNCTION | [email protected] | 2018-09-26 23:33:33 | 2018-09-26 23:33:33 | DEFINER       |         | latin1               | latin1_swedish_ci    | utf8_general_ci    |
+---------+-----------+----------+----------------+---------------------+---------------------+---------------+---------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)

3.查看自定义函数的定义

mysql> show create function simplefun\G;
*************************** 1. row ***************************
            Function: simplefun
            sql_mode:
     Create Function: CREATE DEFINER=`root`@`localhost` FUNCTION `simplefun`() RETURNS varchar(20) CHARSET utf8
RETURN "Hello World!"
character_set_client: latin1
collation_connection: latin1_swedish_ci
  Database Collation: utf8_general_ci
1 row in set (0.00 sec)

4.删除自定义函数

mysql> drop function simplefun;
Query OK, 0 rows affected (0.00 sec)

mysql> show function status\G;
Empty set (0.00 sec)

四.用户管理和授权

 1.创建用户

语法：create user 用户名@主机 identified by 密码；

mysql> create user [email protected] identified by ‘centos‘;
Query OK, 0 rows affected (0.00 sec)
mysql> select user,host,password from user;
+--------+--------------------+-------------------------------------------+
| user   | host               | password                                  |
+--------+--------------------+-------------------------------------------+
| root   | localhost          | *128977E278358FF80A246B5046F51043A2B1FCED |
| root   | centos6.magedu.com |                                           |
| root   | 127.0.0.1          |                                           |
|        | localhost          |                                           |
|        | centos6.magedu.com |                                           |
| momoda | localhost          | *128977E278358FF80A246B5046F51043A2B1FCED |
+--------+--------------------+-------------------------------------------+
6 rows in set (0.01 sec)

2.删除用户

mysql> drop user [email protected];
Query OK, 0 rows affected (0.00 sec)

mysql> select user,host,password from user;
+------+--------------------+-------------------------------------------+
| user | host               | password                                  |
+------+--------------------+-------------------------------------------+
| root | localhost          | *128977E278358FF80A246B5046F51043A2B1FCED |
| root | centos6.magedu.com |                                           |
| root | 127.0.0.1          |                                           |
|      | localhost          |                                           |
|      | centos6.magedu.com |                                           |
+------+--------------------+-------------------------------------------+
5 rows in set (0.00 sec)

 3.授权

grant不仅可以用来授权，还可以用来创建用户；

授权的语法：grant 权限列表 on 库名.表名 to 用户@主机 identified by ‘密码‘;

刷新权限：flush privileges;

mysql>  grant all on *.* to [email protected]‘192.168.%.%‘ identified by ‘123‘;
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> select user,host,password from user;
+------+--------------------+-------------------------------------------+
| user | host               | password                                  |
+------+--------------------+-------------------------------------------+
| root | localhost          | *128977E278358FF80A246B5046F51043A2B1FCED |
| root | centos6.magedu.com |                                           |
| root | 127.0.0.1          |                                           |
|      | localhost          |                                           |
|      | centos6.magedu.com |                                           |
| haha | 192.168.%.%        | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257 |
+------+--------------------+-------------------------------------------+
6 rows in set (0.00 sec)

4.查看授权

mysql> show grants for [email protected]‘192.168.%.%‘;
+------------------------------------------------------------------------------------------------------------------------+
| Grants for [email protected]192.168.%.%                                                                                            |
+------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO ‘haha‘@‘192.168.%.%‘ IDENTIFIED BY PASSWORD ‘*23AE809DDACAF96AF0FD78ED04B6A265E05AA257‘ |
+------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

5.回收授权

回收权限有两种方法：删除用户和revoke

回收语法：  revoke 权限 on 库名.表名 from 用户@主机；

mysql> revoke all on *.* from [email protected]‘192.168.%.%‘;
Query OK, 0 rows affected (0.00 sec)

原文地址：https://www.cnblogs.com/liuwentaolaji/p/9698079.html

时间： 2024-11-09 22:33:33

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