MySQL语法和用户授权

管理数据库   

     create database 等同于 create schema 

     #导入数据库脚本
     MariaDB [db1]> source /root/mysql/hellodb_innodb.sql

管理数据表

数据类型:
    1.数字类型
    2.时间类型
    3.字符串类型

       timestamp 只要表中任何一个字段发生修改,自动存储记录时间精确到秒

      创建表:
          MariaDB [db1]> create table myuser select user,host,password from mysql.user;

      表结构一旦定义好,通常不建议进行修改

      CASCADE 表示级联删除 一般指的是主外键的关系

     选择数据类型
        set      多选
        enum   单选

     复合主键
        primary key(name,city)

    快速删除(不可恢复)
         truncate table students;

    生产环境一般用update标志位来代替删除操作

SQL基础语法

  查询语句写法不同会造成巨大的性能差别,一条很差的查询可能导致服务器宕机

 6记录不是null 7记录才是null  null会在对应的位置显示NULL字符
 不能通过=null来查询, 只能是 is null 或者 is not null来过滤
MariaDB [db1]> select * from students;
+----+------+-------+------+-------+
| id | name | phone | sex  | score |
+----+------+-------+------+-------+
|  1 | aa   | 111   | f    |    80 |
|  2 | bbb  | 2222  | m    |    90 |
|  3 | cccc | 33333 | f    |    80 |
|  4 | ffff | 44444 | m    |    80 |
|  5 | ff   | 555   | f    |    90 |
|  6 | 666  |       | m    |    40 |
|  7 | 777  | NULL  | m    |    40 |

MariaDB [db1]> select sex from students group by sex;
#表示sex这个列有几个不同的值就会被分成几个组
#分完组之后就可以对数据进行相关汇总了
+------+
| sex  |
+------+
| f    |
| m    |
+------+
group by 语法注意点:
  1.select 后面只能加分组的列本身
  2.各种聚合函数

  分组后的过滤条件语法只能使用having 

多个分组
 MariaDB [db1]> select class,sex,avg(score) from students group by class,sex;
+-------+------+------------+
| class | sex  | avg(score) |
+-------+------+------------+
|     1 | f    | 80.0000    |
|     1 | m    | 85.0000    |
|     2 | f    | 60.0000    |
|     2 | m    | 40.0000    |
+-------+------+------------+

 1.内连接 
   取两张表的交集  也可以取多张表的交集
  select s.name,t.name from students s,teachers t where s.teacherid=t.tid;
  select s.name,t.name from students s inner join teachers t on s.teacherid=t.tid;

 2.交叉连接
    两张表的记录分别组合一遍
    select * from students cross join teachers;

 3.左外连接(谁左谁右十分重要)
    默认取左边表的全部记录,取右边表和左边表有交集的记录.

    可取左表和右表没有交集的记录 添加一个过滤条件即可
    and left.id is null

 4.右外连接(谁左谁右十分重要)
   取右边表的全部记录,取左边表和右边表有交集的记录.
   
   取右表记录和左表没有交集的记录
   and right.id is null

 5.自连接 把一张表当成两张表来使用
    select s1.name,s2.name from students as s1 inner join students as s2 on s1.id=s2.id

 6.union连接 竖直排列组合显示
   两个条件:
     1.两个select查询的列的数量必须一致
     2.两个select查询的对应的列的数据类型必须一致
   select id,name from students union select id,name from teachers

 select * from students where stuid in(select stuid from scores where score > (select avg(score) from scores));

select查询语句执行流程

   1.   先执行from 指定对哪张表进行操作
   2.   执行where 过滤表中的行
   3 .  执行group by 分组
   4.   执行having 对分组后的结果过滤
   5.   执行order by 排序
   6.   执行select columns 挑选需要显示的字段
   7.   执行limit 限定需要显示的记录条数

   select查询出来的数据默认是按照磁盘存放次序来排序显示的

   select 语法有点类似于awk

   =  是精确匹配  where name='abc'

   select 可以给字段和表取别名

   like 模糊搜索查询
         %  任意个任意字符
          -   任意单个字符

 MariaDB [db1]> select 'hello word'
    -> ;
+------------+
| hello word |
+------------+
| hello word |
+------------+
1 row in set (0.00 sec)

MariaDB [db1]> select 1+2;
+-----+
| 1+2 |
+-----+
|   3 |
+-----+
MariaDB [db1]> select '1+2',1+2 from user1;
+-----+-----+
| 1+2 | 1+2 |
+-----+-----+
| 1+2 |   3 |
| 1+2 |   3 |
| 1+2 |   3 |
| 1+2 |   3 |
MariaDB [db1]> desc user1;
+----------+----------+------+-----+---------+-------+
| Field    | Type     | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| user     | char(80) | NO   |     |         |       |
| host     | char(60) | NO   |     |         |       |
| password | char(41) | NO   |     |         |       |
+----------+----------+------+-----+---------+-------+

MariaDB [db1]> select user as "姓名",host as "主机" from user1;
+--------+-----------+
| 姓名   | 主机      |
+--------+-----------+
| root   | localhost |
| root   | centos7   |
| root   | 127.0.0.1 |
| root   | ::1       |
+--------+-----------+
 MariaDB [db1]> select class,sex,avg(score) from students group by class,sex;
+-------+------+------------+
| class | sex  | avg(score) |
+-------+------+------------+
|     1 | f    | 80.0000    |
|     1 | m    | 85.0000    |
|     2 | f    | 60.0000    |
|     2 | m    | 40.0000    |
+-------+------+------------+
MariaDB [hellodb]> select s.name,sc.score,c.course from students s,scores sc,courses c where s.stuid=sc.stuid and sc.courseid=c.courseid limit 5;
+-------------+-------+----------------+
| name        | score | course         |
+-------------+-------+----------------+
| Shi Zhongyu |    77 | Kuihua Baodian |
| Shi Zhongyu |    93 | Weituo Zhang   |
| Shi Potian  |    47 | Kuihua Baodian |
| Shi Potian  |    97 | Daiyu Zanghua  |
| Xie Yanke   |    88 | Kuihua Baodian |
+-------------+-------+----------------+


MariaDB [hellodb]> select s.name,sc.score,c.course from (select * from students limit 5) s,scores sc,courses c where s.stuid=sc.stuid and sc.courseid=c.courseid;
+-------------+-------+----------------+
| name        | score | course         |
+-------------+-------+----------------+
| Shi Zhongyu |    77 | Kuihua Baodian |
| Shi Zhongyu |    93 | Weituo Zhang   |
| Shi Potian  |    47 | Kuihua Baodian |
| Shi Potian  |    97 | Daiyu Zanghua  |
| Xie Yanke   |    88 | Kuihua Baodian |
| Xie Yanke   |    75 | Weituo Zhang   |
| Ding Dian   |    71 | Daiyu Zanghua  |
| Ding Dian   |    89 | Kuihua Baodian |
| Yu Yutong   |    39 | Hamo Gong      |
| Yu Yutong   |    63 | Dagou Bangfa   |
+-------------+-------+----------------+

MariaDB [hellodb]> select re.name,avg(score) from (select s.name,sc.score,c.course from (select * from students limit 8) s,scores sc,courses c where s.stuid=sc.stuid and sc.courseid=c.courseid ) as re group by name order by avg(score) desc;
+-------------+------------+
| name        | avg(score) |
+-------------+------------+
| Shi Qing    | 96.0000    |
| Shi Zhongyu | 85.0000    |
| Xi Ren      | 84.5000    |
| Xie Yanke   | 81.5000    |
| Ding Dian   | 80.0000    |
| Lin Daiyu   | 75.0000    |
| Shi Potian  | 72.0000    |
| Yu Yutong   | 51.0000    |
+-------------+------------+

MariaDB [hellodb]> select c.course,re.stucount from courses as c,(select courseid,count(stuid) as stucount from scores group by courseid) as re where c.courseid=re.courseid;
+----------------+----------+
| course         | stucount |
+----------------+----------+
| Hamo Gong      |        3 |
| Kuihua Baodian |        4 |
| Jinshe Jianfa  |        1 |
| Taiji Quan     |        1 |
| Daiyu Zanghua  |        2 |
| Weituo Zhang   |        2 |
| Dagou Bangfa   |        2 |
+----------------+----------+

MariaDB [hellodb]> select * from students where age > (select avg(age) from students);
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     3 | Xie Yanke    |  53 | M      |       2 |        16 |
|     4 | Ding Dian    |  32 | M      |       4 |         4 |
|     6 | Shi Qing     |  46 | M      |       5 |      NULL |
|    13 | Tian Boguang |  33 | M      |       2 |      NULL |
|    25 | Sun Dasheng  | 100 | M      |    NULL |      NULL |
+-------+--------------+-----+--------+---------+-----------+

MariaDB [hellodb]> select name from students where stuid in(select stuid from scores where courseid in(1,2,4,7));
+-------------+
| name        |
+-------------+
| Shi Zhongyu |
| Shi Potian  |
| Xie Yanke   |
| Ding Dian   |
| Yu Yutong   |
| Shi Qing    |
| Xi Ren      |
| Lin Daiyu   |
+-------------+
MariaDB [hellodb]> select s.name,s.age from students s,(select classid,avg(age) as age,count(stuid)from students group by classid having count(stuid)>=3) as re where s.classid = re.classid and s.age > re.age;
+---------------+-----+
| name          | age |
+---------------+-----+
| Shi Potian    |  22 |
| Xie Yanke     |  53 |
| Ding Dian     |  32 |
| Yu Yutong     |  26 |
| Yuan Chengzhi |  23 |
| Xu Zhu        |  21 |
| Lin Chong     |  25 |
| Hua Rong      |  23 |
| Huang Yueying |  22 |
+---------------+-----+
9 rows in set (0.00 sec)

视图

   VIEW,虚表        保存有实表的查询结果 

   视图中的数据事实上存储于“基表”中    因此,其修改操作也会针对基表实现; 其修改操作受基表限制

函数

      系统函数和自定义函数   保存在mysql.proc表中 

存储过程

      存储过程           存储过程保存在mysql.proc表中 

触发器

      trigger_name：触发器的名称

      trigger_time：{ BEFORE | AFTER },表示在事件之前或之后触发

      trigger_event:：{ INSERT |UPDATE | DELETE },触发的具体事件

      tbl_name：该触发器作用在表名 

      触发器的执行不是由程序调用,   也不是由手工启动,而是由事件来触发,激活从而实现执行 

      触发器实例,在向学生表INSERT数据时,学生数增加,DELETE学生时,学生数减少 

   

 MySQL用户和授权管理

     用户管理

    创建用户：CREATE USER 

    CREATE USER 'USERNAME'@'HOST' [IDENTIFIED BY 'password']；  默认权限：USAGE   只能连接不能进行任何操作

    用户重命名：RENAME USER  RENAME USER old_user_name TO new_user_name

    删除用户：  DROP USER 'USERNAME'@'HOST‘   

    示例：删除默认的空用户  DROP USER ''@'localhost'; 

   修改密码：

      mysql>SET PASSWORD FOR 'user'@'host' = PASSWORD(‘password');

      mysql>UPDATE mysql.user SET password=PASSWORD('your_password') WHERE clause;   

      此方法需要执行下面指令才能生效：mysql> FLUSH PRIVILEGES; 

     #mysqladmin -u root –poldpass  password  ‘newpass‘

     忘记管理员密码的解决办法：

             启动mysqld进程时,为其使用如下选项:  --skip-grant-tables --skip-networking  修改配置文件/etc/my.cnf中的mysqld

             使用UPDATE命令修改管理员密码

             关闭mysqld进程,移除上述两个选项,重启mysqld

   权限管理

     授权和创建用户可以都通过grant命令一步来实现,因为grant授权的用户如果不存在,mysql会自动创建对应的用户

     权限类别：

         1.数据库级别

         2.表级别

         3.字段级别

         4.管理类

         5.程序类

    授权语法:

       GRANT priv_type [(column_list)],... ON [object_type] priv_level TO 'user'@'host' [IDENTIFIED BY 'password']

       priv_type: ALL [PRIVILEGES] 

       object_type:TABLE | FUNCTION | PROCEDURE 

       priv_level:  *(所有库)  | *.*  | db_name.*  | db_name.tbl_name  | tbl_name(当前库的表)  | db_name.routine_name(指定库的函数,存储过程,触发器) 

       GRANT SELECT (col1), INSERT (col1,col2) ON mydb.mytbl TO 'someuser'@'somehost';

       MariaDB [(none)]> grant all on hellodb.* to yxh@"192.168.%.%" identified by 'root';
       MariaDB [(none)]> grant select,insert on hellodb.* to laoge@'%' identified by 'root';

       MariaDB [(none)]> grant select(stuid,name) on hellodb.students to dage@'%' identified by 'root';

       MariaDB [(none)]> show grants for yxh@"192.168.%.%";

    回收授权语法:

           REVOKE   priv_type [(column_list)]  [, priv_type [(column_list)]] ...    ON [object_type] priv_level  FROM user [, user] ... 

           示例:   REVOKE  DELETE  ON   testdb.*   FROM   'testuser'@'%'

    查看用户的授权信息:

          Help SHOW GRANTS

          SHOW GRANTS FOR 'user'@'host'; 

          SHOW GRANTS FOR CURRENT_USER[()]; 

         注意：MariaDB服务进程启动时会读取mysql库中所有授权表至内存

                  (1) GRANT或REVOKE等执行权限操作会保存于系统表中,MariaDB的服务进程通常会自动重读授权表,使之生效

                  (2) 对于不能够或不能及时重读授权表的命令,可手动让MariaDB的服务进程重读授权表

                       mysql> FLUSH PRIVILEGES;