MySQL数据库（五）视图、函数，存储过程，触发器，事件

1 VIEW 视图

视图：虚拟表，保存有实表的查询结果，相当于别名
创建方法：

CREATE VIEW view_name [(column_list)]
		AS select_statement
		[WITH [CASCADED | LOCAL] CHECK OPTION]

查看视图定义：

SHOW CREATE VIEW view_name #只能看视图定义
SHOW CREATE TABLE view_name # 可以查看表和视图

删除视图：

DROP VIEW [IF EXISTS]
		view_name [, view_name] ...
		[RESTRICT | CASCADE]

注意：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

范例：

MariaDB [hellodb]> create view v_score as select st.name,co.Course,sc.score from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=co.courseid;
Query OK, 0 rows affected (0.002 sec)

MariaDB [hellodb]> select * from v;
ERROR 1146 (42S02): Table 'hellodb.v' doesn't exist
MariaDB [hellodb]> select * from v_score;
+-------------+----------------+-------+
| name        | Course         | score |
+-------------+----------------+-------+
| Shi Zhongyu | Kuihua Baodian |    77 |
| Shi Zhongyu | Weituo Zhang   |    93 |
| Shi Potian  | Kuihua Baodian |    47 |
| Shi Potian  | Daiyu Zanghua  |    97 |
| Xie Yanke   | Kuihua Baodian |    88 |
| Xie Yanke   | Weituo Zhang   |    75 |
| Ding Dian   | Daiyu Zanghua  |    71 |
| Ding Dian   | Kuihua Baodian |    89 |
| Yu Yutong   | Hamo Gong      |    39 |
| Yu Yutong   | Dagou Bangfa   |    63 |
| Shi Qing    | Hamo Gong      |    96 |
| Xi Ren      | Hamo Gong      |    86 |
| Xi Ren      | Dagou Bangfa   |    83 |
| Lin Daiyu   | Taiji Quan     |    57 |
| Lin Daiyu   | Jinshe Jianfa  |    93 |
+-------------+----------------+-------+
15 rows in set (0.001 sec)

MariaDB [hellodb]> SHOW TABLE STATUS LIKE 'v_score'\G
*************************** 1. row ***************************
            Name: v_score
          Engine: NULL
         Version: NULL
      Row_format: NULL
            Rows: NULL
  Avg_row_length: NULL
     Data_length: NULL
 Max_data_length: NULL
    Index_length: NULL
       Data_free: NULL
  Auto_increment: NULL
     Create_time: NULL
     Update_time: NULL
      Check_time: NULL
       Collation: NULL
        Checksum: NULL
  Create_options: NULL
         Comment: VIEW
Max_index_length: NULL
       Temporary: NULL
1 row in set (0.001 sec)

[root@centos8 ~]#ls /var/lib/mysql/hellodb/
classes.frm  courses.frm  emp.ibd       students.ibd   teachers.ibd
classes.ibd  courses.ibd  scores.frm    teachers2.frm  toc.frm
coc.frm      db.opt       scores.ibd    teachers2.ibd  toc.ibd
coc.ibd      emp.frm      students.frm  teachers.frm   v_score.frm

2 FUNCTI

ON 函数
函数：分为系统内置函数和自定义函数

• 系统内置函数参考：
  https://dev.mysql.com/doc/refman/5.7/en/func-op-summary-ref.html
• 自定义函数：user-defined function UDF，保存在mysql.proc表中

创建UDF语法

CREATE [AGGREGATE] FUNCTION function_name(parameter_name type,[parameter_name
type,...])
	RETURNS {STRING|INTEGER|REAL}
	runtime_body

说明：

• 参数可以有多个,也可以没有参数
• 无论有无参数，小括号（）是必须的
• 必须有且只有一个返回值

查看函数列表：

SHOW FUNCTION STATUS;

查看函数定义

SHOW CREATE FUNCTION function_name

删除UDF

DROP FUNCTION function_name

调用自定义函数语法

SELECT function_name(parameter_value,...)

范例：

#无参UDF
CREATE FUNCTION simpleFun() RETURNS VARCHAR(20) RETURN "Hello World";

#有参数UDF
DELIMITER //

CREATE FUNCTION deleteById(id SMALLINT UNSIGNED) RETURNS VARCHAR(20)
BEGIN
	DELETE FROM students WHERE stuid = id;
	RETURN (SELECT COUNT(*) FROM students);
END//

DELIMITER ;

MySQL中的变量

两种变量：系统内置变量和用户自定义变量

• 系统变量：MySQL数据库中内置的变量，可用@@var_name引用
• 用户自定义变量分为以下两种
  • 普通变量：在当前会话中有效，可用@var_name引用
  • 局部变量：在函数或存储过程内才有效，需要用DECLARE 声明，之后直接用 var_name引用

自定义函数中定义局部变量语法

DECLARE 变量1[,变量2,... ]变量类型 [DEFAULT 默认值]

说明：局部变量的作用范围是在BEGIN…END程序中,而且定义局部变量语句必须在BEGIN…END的第一行定义

范例:

DELIMITER //
CREATE FUNCTION addTwoNumber(x SMALLINT UNSIGNED, y SMALLINT UNSIGNED)
RETURNS SMALLINT
BEGIN
	DECLARE a, b SMALLINT UNSIGNED;
	SET a = x, b = y;
	RETURN a+b;
END//
DELIMITER ;

MariaDB [hellodb]> select addTwoNumber(10,20);
+---------------------+
| addTwoNumber(10,20) |
+---------------------+
|                  30 |
+---------------------+
1 row in set (0.000 sec)

为变量赋值语法

SET parameter_name = value[,parameter_name = value...]
SELECT INTO parameter_name

范例:

.....
DECLARE x int;
SELECT COUNT(*) FROM tdb_name INTO x;
RETURN x;
END//

范例：自定义的普通变量

3 PROCEDURE 存储过程

存储过程：多表SQL的语句的集合，可以独立执行，存储过程保存在mysql.proc表中

存储过程优势：
存储过程把经常使用的SQL语句或业务逻辑封装起来,预编译保存在数据库中,当需要时从数据库中直接调用,省去了编译的过程，提高了运行速度，同时降低网络数据传输量

存储过程与自定义函数的区别
存储过程实现的过程要复杂一些,而函数的针对性较强
存储过程可以有多个返回值,而自定义函数只有一个返回值
存储过程一般可独立执行,而函数往往是作为其他SQL语句的一部分来使用

创建存储过程

CREATE PROCEDURE sp_name ([ proc_parameter [,proc_parameter ...]])
routime_body

proc_parameter : [IN|OUT|INOUT] parameter_name type

说明：其中IN表示输入参数，OUT表示输出参数，INOUT表示既可以输入也可以输出；param_name 表示参数名称；type表示参数的类型

查看存储过程列表

SHOW PROCEDURE STATUS;

查看存储过程定义

SHOW CREATE PROCEDURE sp_name

调用存储过程

CALL sp_name ([ proc_parameter [,proc_parameter ...]])

说明:当无参时,可以省略"()",当有参数时,不可省略"()”

存储过程修改

ALTER语句修改存储过程只能修改存储过程的注释等无关紧要的东西,不能修改存储过程体,所以要修改存储过程,方法就是删除重建

删除存储过程

DROP PROCEDURE [IF EXISTS] sp_name

范例

# 创建无参存储过程
delimiter //
CREATE PROCEDURE showTime()
BEGIN
	SELECT now();
END//
delimiter ;

CALL showTime;

范例

#创建含参存储过程：只有一个IN参数
delimiter //
CREATE PROCEDURE selectById(IN id SMALLINT UNSIGNED)
BEGIN
	SELECT * FROM students WHERE stuid = id;
END//
delimiter ;
call selectById(2);

范例

delimiter //
CREATE PROCEDURE dorepeat(n INT)
BEGIN
	SET @i = 0;
	SET @sum = 0;
	REPEAT SET @sum = @sum+@i;
	SET @i = @i + 1;
	UNTIL @i > n END REPEAT;
END//
delimiter ;
CALL dorepeat(100);
SELECT @sum;

范例

#创建含参存储过程:包含IN参数和OUT参数
delimiter //
CREATE PROCEDURE deleteById(IN id SMALLINT UNSIGNED, OUT num SMALLINT UNSIGNED)
BEGIN
DELETE FROM students WHERE stuid >= id;
SELECT row_count() into num;
END//
delimiter ;
call deleteById(2,@Line);
SELECT @Line;
#说明:创建存储过程deleteById,包含一个IN参数和一个OUT参数.调用时,传入删除的ID和保存被修改的行数值的用户变量@Line,select @Line;输出被影响行数
#row_count() 系统内置函数，用于存放前一条SQL修改过的表的记录数

流程控制

存储过程和函数中可以使用流程控制来控制语句的执行

• IF：用来进行条件判断。根据是否满足条件，执行不同语句
• CASE：用来进行条件判断，可实现比IF语句更复杂的条件判断
• LOOP：重复执行特定的语句，实现一个简单的循环
• LEAVE：用于跳出循环控制，相当于SHELL中break
• ITERATE：跳出本次循环，然后直接进入下一次循环，相当于SHELL中continue
• REPEAT：有条件控制的循环语句。当满足特定条件时，就会跳出循环语句
• WHILE：有条件控制的循环语句

4 TRIGGER触发器

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

创建触发器

CREATE [DEFINER = { user | CURRENT_USER }]
	TRIGGER trigger_name
	trigger_time trigger_event
	ON tbl_name FOR EACH ROW
	trigger_body

说明：
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

范例：

#创建触发器，在向学生表INSERT数据时，学生数增加，DELETE学生时，学生数减少
CREATE TABLE student_info (
	stu_id INT(11) NOT NULL AUTO_INCREMENT ,
	stu_name VARCHAR(255) DEFAULT NULL,
	PRIMARY KEY (stu_id)
);
CREATE TABLE student_count (
	student_count INT(11) DEFAULT 0
);
INSERT INTO student_count VALUES(0);
CREATE TRIGGER trigger_student_count_insert
AFTER INSERT
ON student_info FOR EACH ROW
UPDATE student_count SET student_count=student_count+1;
CREATE TRIGGER trigger_student_count_delete
AFTER DELETE
ON student_info FOR EACH ROW
UPDATE student_count SET student_count=student_count-1;

[root@centos8 ~]#cat /var/lib/mysql/hellodb/trigger_student_count_delete.TRN 
TYPE=TRIGGERNAME
trigger_table=student_info
[root@centos8 ~]#cat /var/lib/mysql/hellodb/trigger_student_count_insert.TRN 
TYPE=TRIGGERNAME
trigger_table=student_info
[root@centos8 ~]#cat /var/lib/mysql/hellodb/student_info.TRG 
TYPE=TRIGGERS
triggers='CREATE DEFINER=`root`@`localhost` TRIGGER trigger_student_count_insert\nAFTER INSERT\nON student_info FOR EACH ROW\nUPDATE student_count SET student_count=student_count+1' 'CREATE DEFINER=`root`@`localhost` TRIGGER trigger_student_count_delete\nAFTER DELETE\nON student_info FOR EACH ROW\nUPDATE student_count SET student_count=student_count-1'
sql_modes=1411383296 1411383296
definers='root@localhost' 'root@localhost'
client_cs_names='utf8' 'utf8'
connection_cl_names='utf8_general_ci' 'utf8_general_ci'
db_cl_names='utf8_general_ci' 'utf8_general_ci'
created=159142866954 159142867177

MariaDB [hellodb]> select * from student_info;
Empty set (0.001 sec)

MariaDB [hellodb]> select * from student_count;
+---------------+
| student_count |
+---------------+
|             0 |
+---------------+
1 row in set (0.000 sec)

MariaDB [hellodb]> insert student_info (stu_name)value('xioaming');
Query OK, 1 row affected (0.002 sec)

MariaDB [hellodb]> select * from student_info;
+--------+----------+
| stu_id | stu_name |
+--------+----------+
|      1 | xioaming |
+--------+----------+
1 row in set (0.001 sec)

MariaDB [hellodb]> select * from student_count;
+---------------+
| student_count |
+---------------+
|             1 |
+---------------+
1 row in set (0.000 sec)

MariaDB [hellodb]> insert student_info (stu_name)value('xiaohong');
Query OK, 1 row affected (0.001 sec)

MariaDB [hellodb]> insert student_info (stu_name)value('xiaoqiang'),('wangcai');
Query OK, 2 rows affected (0.002 sec)
Records: 2  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> select * from student_info;
+--------+-----------+
| stu_id | stu_name  |
+--------+-----------+
|      1 | xioaming  |
|      2 | xiaohong  |
|      3 | xiaoqiang |
|      4 | wangcai   |
+--------+-----------+
4 rows in set (0.000 sec)

MariaDB [hellodb]> select * from student_count;
+---------------+
| student_count |
+---------------+
|             4 |
+---------------+
1 row in set (0.000 sec)

MariaDB [hellodb]> delete from student_info where stu_id >= 3;
Query OK, 2 rows affected (0.001 sec)

MariaDB [hellodb]> select * from student_count;
+---------------+
| student_count |
+---------------+
|             2 |
+---------------+
1 row in set (0.000 sec)

MariaDB [hellodb]> select * from student_info;
+--------+----------+
| stu_id | stu_name |
+--------+----------+
|      1 | xioaming |
|      2 | xiaohong |
+--------+----------+
2 rows in set (0.000 sec)

查看触发器

#在当前数据库对应的目录下，可以查看到新生成的相关文件：trigger_name.TRN,table _name.TRG
SHOW TRIGGERS;
#查询系统表information_schema.triggers的方式指定查询条件，查看指定的触发器信息。
USE information_schema;
SELECT * FROM triggers WHERE trigger_name='trigger_student_count_insert';

删除触发器

DROP TRIGGER trigger_name;

5 Event 事件

5.1 Event 事件介绍

事件（event）是MySQL在相应的时刻调用的过程式数据库对象。一个事件可调用一次，也可周期性的启动，它由一个特定的线程来管理的，也就是所谓的“事件调度器”。

事件和触发器类似，都是在某些事情发生的时候启动。当数据库上启动一条语句的时候，触发器就启动了，而事件是根据调度事件来启动的。由于它们彼此相似，所以事件也称为临时性触发器。

事件取代了原先只能由操作系统的计划任务来执行的工作，而且MySQL的事件调度器可以精确到每秒钟执行一个任务，而操作系统的计划任务（如：Linux下的CRON或Windows下的任务计划）只能精确到每分钟执行一次。

事件的优缺点

优点：一些对数据定时性操作不再依赖外部程序，而直接使用数据库本身提供的功能，可以实现每秒钟执行一个任务，这在一些对实时性要求较高的环境下就非常实用

缺点：定时触发，不可以直接调用

5.2 Event 管理

5.2.1 相关变量和服务器选项

MySQL事件调度器event_scheduler负责调用事件，它默认是关闭的。这个调度器不断地监视一个事件是否要调用， 要创建事件，必须打开调度器

服务器系统变量和服务器选项：
event_scheduler：默认值为OFF，设置为ON才支持Event，并且系统自动打开专用的线程

范例：开启和关闭event_scheduler

#默认事件调度功能是关闭的
MariaDB [(none)]> select @@event_scheduler;
+-------------------+
| @@event_scheduler |
+-------------------+
| OFF               |
+-------------------+
1 row in set (0.000 sec)

#临时开启事件调度功能
MariaDB [(none)]> set global event_scheduler=1;
Query OK, 0 rows affected (0.000 sec)

MariaDB [(none)]> show processlist;
+----+-----------------+-----------+------+---------+------+--------------------------+------------------+----------+
| Id | User            | Host      | db   | Command | Time | State                    | Info             | Progress |
+----+-----------------+-----------+------+---------+------+--------------------------+------------------+----------+
|  1 | system user     |           | NULL | Daemon  | NULL | InnoDB purge coordinator | NULL             |    0.000 |
|  2 | system user     |           | NULL | Daemon  | NULL | InnoDB purge worker      | NULL             |    0.000 |
|  4 | system user     |           | NULL | Daemon  | NULL | InnoDB purge worker      | NULL             |    0.000 |
|  3 | system user     |           | NULL | Daemon  | NULL | InnoDB purge worker      | NULL             |    0.000 |
|  5 | system user     |           | NULL | Daemon  | NULL | InnoDB shutdown handler  | NULL             |    0.000 |
|  6 | event_scheduler | localhost | NULL | Daemon  | 2166 | Waiting on empty queue   | NULL             |    0.000 |
| 10 | root            | localhost | NULL | Query   |    0 | Init                     | show processlist |    0.000 |
+----+-----------------+-----------+------+---------+------+--------------------------+------------------+----------+
7 rows in set (0.000 sec)

#临时关闭事件调度功能
MariaDB [(none)]> set global event_scheduler=0;
Query OK, 0 rows affected (0.000 sec)

MariaDB [(none)]> show processlist;
+----+-------------+-----------+------+---------+------+--------------------------+------------------+----------+
| Id | User        | Host      | db   | Command | Time | State                    | Info             | Progress |
+----+-------------+-----------+------+---------+------+--------------------------+------------------+----------+
|  1 | system user |           | NULL | Daemon  | NULL | InnoDB purge coordinator | NULL             |    0.000 |
|  2 | system user |           | NULL | Daemon  | NULL | InnoDB purge worker      | NULL             |    0.000 |
|  4 | system user |           | NULL | Daemon  | NULL | InnoDB purge worker      | NULL             |    0.000 |
|  3 | system user |           | NULL | Daemon  | NULL | InnoDB purge worker      | NULL             |    0.000 |
|  5 | system user |           | NULL | Daemon  | NULL | InnoDB shutdown handler  | NULL             |    0.000 |
| 10 | root        | localhost | NULL | Query   |    0 | Init                     | show processlist |    0.000 |
+----+-------------+-----------+------+---------+------+--------------------------+------------------+----------+
6 rows in set (0.000 sec)

#持久开启事件调度
[root@centos8 ~]#vim /etc/my.cnf.d/mariadb-server.cnf
[mysqld]
event_scheduler=ON
[root@centos8 ~]#systemctl restart mariadb

5.2.2 管理事件

create event 语句创建一个事件。每个事件由两个主要部分组成，第一部分是事件调度（event schedule），表示事件何时启动以及按什么频率启动，第二部分是事件动作（event action ），这是事件启动时执行的代码，事件的动作包含一条SQL语句，它可能是一个简单地insert或者update语句，也可以使一个存储过程或者 benin…end语句块，这两种情况允许我们执行多条SQL

一个事件可以是活动（打开）的或停止（关闭）的，活动意味着事件调度器检查事件动作是否必须调用，停止意味着事件的声明存储在目录中，但调度器不会检查它是否应该调用。在一个事件创建之后，它立即变为活动的，一个活动的事件可以执行一次或者多次

创建Event

CREATE
    [DEFINER = { user | CURRENT_USER }]
    EVENT
    [IF NOT EXISTS]
    event_name
    ON SCHEDULE schedule
    [ON COMPLETION [NOT] PRESERVE]
    [ENABLE | DISABLE | DISABLE ON SLAVE]
    [COMMENT 'comment']
    DO event_body;

schedule:
    AT timestamp [+ INTERVAL interval] ...
  | EVERY interval
    [STARTS timestamp [+ INTERVAL interval] ...]
    [ENDS timestamp [+ INTERVAL interval] ...]

interval:
    quantity {YEAR | QUARTER | MONTH | DAY | HOUR | MINUTE |
              WEEK | SECOND | YEAR_MONTH | DAY_HOUR | DAY_MINUTE |
              DAY_SECOND | HOUR_MINUTE | HOUR_SECOND | MINUTE_SECOND}

说明：

• event_name ：创建的event名字，必须是唯一确定的
  ON SCHEDULE：计划任务
• schedule: 决定event的执行时间和频率（注意时间一定要是将来的时间，过去的时间会出错），有两种形式 AT和EVERY
• [ON COMPLETION [NOT] PRESERVE]： 可选项，默认是ON COMPLETION NOT PRESERVE 即计划任务执行完毕后自动drop该事件；ON COMPLETION PRESERVE则不会drop掉
• [COMMENT ‘comment’] ：可选项，comment 用来描述event；相当注释，最大长度64个字节
• [ENABLE | DISABLE] ：设定event的状态，默认ENABLE：表示系统尝试执行这个事件， DISABLE：关闭该事情，可以用alter修改
• DO event_body: 需要执行的sql语句，可以是复合语句

提示：event事件是存放在mysql.event表中

查看Event

SHOW EVENTS [{FROM | IN} schema_name]
[LIKE 'pattern' | WHERE expr]

注意：事件执行完即释放，如立即执行事件，执行完后，事件便自动删除，多次调用事件或等待执行事件,才可以用上述命令查看到。

修改Event

ALTER
    [DEFINER = { user | CURRENT_USER }]
    EVENT event_name
    [ON SCHEDULE schedule]
    [ON COMPLETION [NOT] PRESERVE]
    [RENAME TO new_event_name]
    [ENABLE | DISABLE | DISABLE ON SLAVE]
    [COMMENT 'comment']
    [DO event_body]

注意：alter event语句可以修改事件的定义和属性。可以让一个事件成为停止的或者再次让它活动，也可以修改一个事件的名字或者整个调度。然而当一个使用 ON COMPLETION NOT PRESERVE 属性定义的事件最后一次执行后，事件直接就不存在了，不能修改

删除Event

DROP EVENT [IF EXISTS] event_name

5.2.3 范例

范例：创建立即启动事件

MariaDB [(none)]> create database testdb;
Query OK, 1 row affected (0.000 sec)
MariaDB [(none)]> use testdb
Database changed
#创建一个表记录每次事件调度的名字和事件戳
MariaDB [testdb]> create table events_list(event_name varchar(20) not null,event_started timestamp not null);
Query OK, 0 rows affected (0.006 sec)

#临时关闭事件调度功能
MariaDB [testdb]> set global event_scheduler=0;
Query OK, 0 rows affected (0.000 sec)
MariaDB [testdb]> show variables like 'event_scheduler';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| event_scheduler | OFF   |
+-----------------+-------+
1 row in set (0.001 sec)

#创建一次性事件
MariaDB [testdb]> create event event_now on schedule at now() do insert into events_list values('event_now', now());
Query OK, 0 rows affected, 1 warning (0.000 sec)

#因为事件调度功能禁用，所有表中无记录
MariaDB [testdb]> select *from events_list;
Empty set (0.001 sec)

#查看事件
MariaDB [testdb]> show events\G
*************************** 1. row ***************************
                  Db: testdb
                Name: event_now
             Definer: root@localhost
           Time zone: SYSTEM
                Type: ONE TIME
          Execute at: 2020-06-06 16:52:08
      Interval value: NULL
      Interval field: NULL
              Starts: NULL
                Ends: NULL
              Status: ENABLED
          Originator: 1
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: latin1_swedish_ci
1 row in set (0.001 sec)

#任务计划存放在mysql.event表中
MariaDB [testdb]> select * from mysql.event\G
*************************** 1. row ***************************
                  db: testdb
                name: event_now
                body: insert into events_list values('event_now', now())
             definer: root@localhost
          execute_at: 2020-06-06 08:52:08
      interval_value: NULL
      interval_field: NULL
             created: 2020-06-06 16:52:08
            modified: 2020-06-06 16:52:08
       last_executed: NULL
              starts: NULL
                ends: NULL
              status: ENABLED
       on_completion: DROP
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             comment: 
          originator: 1
           time_zone: SYSTEM
character_set_client: utf8
collation_connection: utf8_general_ci
        db_collation: latin1_swedish_ci
           body_utf8: insert into events_list values('event_now', now())
1 row in set (0.000 sec)

#开启事件调度功能
MariaDB [testdb]> set global event_scheduler=1;
Query OK, 0 rows affected (0.000 sec)
#事件立即执行，每秒插入一条记录
MariaDB [testdb]> select *from events_list;
+------------+---------------------+
| event_name | event_started       |
+------------+---------------------+
| event_now  | 2020-06-06 16:52:39 |
+------------+---------------------+
1 row in set (0.000 sec)

#事件执行完成后自动删除
MariaDB [testdb]> show events;
Empty set (0.001 sec)

范例：创建每秒启动的事件

#创建一个表记录每次事件调度的名字和事件戳
MariaDB [testdb]> create table events_list(event_name varchar(20) not null,event_started timestamp not null);
Query OK, 0 rows affected (0.005 sec)

#开启事件调度功能
MariaDB [testdb]> set global event_scheduler=1;
Query OK, 0 rows affected (0.000 sec)

#创建事件
MariaDB [testdb]> CREATE EVENT event_every_second ON SCHEDULE EVERY 1 SECOND DO INSERT INTO events_list VALUES('event_now', now());
Query OK, 0 rows affected, 1 warning (0.000 sec)

MariaDB [testdb]> SHOW EVENTS\G
*************************** 1. row ***************************
                  Db: testdb
                Name: event_every_second
             Definer: root@localhost
           Time zone: SYSTEM
                Type: RECURRING
          Execute at: NULL
      Interval value: 1
      Interval field: SECOND
              Starts: 2020-06-06 17:27:44
                Ends: NULL
              Status: ENABLED
          Originator: 1
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: latin1_swedish_ci
1 row in set (0.001 sec)

#事件是存放在mysql.event表中
MariaDB [testdb]> select *from mysql.event\G
*************************** 1. row ***************************
                  db: testdb
                name: event_every_second
                body: INSERT INTO events_list VALUES('event_now', now())
             definer: root@localhost
          execute_at: NULL
      interval_value: 1
      interval_field: SECOND
             created: 2020-06-06 17:27:44
            modified: 2020-06-06 17:27:44
       last_executed: NULL
              starts: 2020-06-06 09:27:44
                ends: NULL
              status: ENABLED
       on_completion: DROP
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             comment: 
          originator: 1
           time_zone: SYSTEM
character_set_client: utf8
collation_connection: utf8_general_ci
        db_collation: latin1_swedish_ci
           body_utf8: INSERT INTO events_list VALUES('event_now', now())
1 row in set (0.000 sec)


MariaDB [testdb]> select *from events_list;
+------------+---------------------+
| event_name | event_started       |
+------------+---------------------+
| event_now  | 2020-06-06 17:28:09 |
| event_now  | 2020-06-06 17:28:10 |
| event_now  | 2020-06-06 17:28:11 |
| event_now  | 2020-06-06 17:28:12 |
| event_now  | 2020-06-06 17:28:13 |
| event_now  | 2020-06-06 17:28:14 |
| event_now  | 2020-06-06 17:28:15 |
| event_now  | 2020-06-06 17:28:16 |
| event_now  | 2020-06-06 17:28:17 |
| event_now  | 2020-06-06 17:28:18 |
| event_now  | 2020-06-06 17:28:19 |
| event_now  | 2020-06-06 17:28:20 |
| event_now  | 2020-06-06 17:28:21 |
| event_now  | 2020-06-06 17:28:22 |
+------------+---------------------+
14 rows in set (0.000 sec)

MariaDB [testdb]> drop event event_every_second;
Query OK, 0 rows affected (0.000 sec)

MariaDB [testdb]> SHOW EVENTS\G
Empty set (0.001 sec)

MariaDB [testdb]> select *from mysql.event\G
Empty set (0.000 sec)

范例： 创建每分钟启动的事件

MariaDB [testdb]> show variables like 'event_scheduler';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| event_scheduler | ON    |
+-----------------+-------+
1 row in set (0.001 sec)

MariaDB [testdb]> create event testdb.event_every_minute on schedule every 1 minute do insert into events_list values('event_now', now());
Query OK, 0 rows affected (0.000 sec)

MariaDB [testdb]> select now();
+---------------------+
| now()               |
+---------------------+
| 2020-06-06 17:34:30 |
+---------------------+
1 row in set (0.000 sec)

MariaDB [testdb]> select *from events_list;
+------------+---------------------+
| event_name | event_started       |
+------------+---------------------+
| event_now  | 2020-06-06 17:34:26 |
+------------+---------------------+
20 rows in set (0.000 sec)

MariaDB [testdb]> SHOW EVENTS\G
*************************** 1. row ***************************
                  Db: testdb
                Name: event_every_minute
             Definer: root@localhost
           Time zone: SYSTEM
                Type: RECURRING
          Execute at: NULL
      Interval value: 1
      Interval field: MINUTE
              Starts: 2020-06-06 17:34:26
                Ends: NULL
              Status: ENABLED
          Originator: 1
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: latin1_swedish_ci
1 row in set (0.001 sec)

MariaDB [testdb]> select *from events_list;
+------------+---------------------+
| event_name | event_started       |
+------------+---------------------+
| event_now  | 2020-06-06 17:34:26 |
| event_now  | 2020-06-06 17:35:26 |
| event_now  | 2020-06-06 17:36:26 |
| event_now  | 2020-06-06 17:37:26 | 
| event_now  | 2020-06-06 17:38:26 |
| event_now  | 2020-06-06 17:39:26 |
| event_now  | 2020-06-06 17:40:26 |
| event_now  | 2020-06-06 17:41:26 |
| event_now  | 2020-06-06 17:42:26 |
+------------+---------------------+
9 rows in set (0.000 sec)

范例：创建定时调用存储过程的事件

MariaDB [testdb]> drop event event_every_minute;
Query OK, 0 rows affected (0.000 sec)

MariaDB [testdb]> truncate table events_list;
Query OK, 0 rows affected (0.007 sec)

MariaDB [testdb]> select *from events_list;
Empty set (0.000 sec)

MariaDB [testdb]> delimiter //
MariaDB [testdb]>  create procedure sp_insert()
    -> begin
    -> insert into events_list values('event_now', now());
    -> end//
Query OK, 0 rows affected (0.000 sec)

MariaDB [testdb]> delimiter ;
MariaDB [testdb]> CREATE DEFINER=`root`@`localhost` EVENT event_test ON SCHEDULE EVERY 10 SECOND STARTS '2019-12-02 22:55:00' ON COMPLETION PRESERVE ENABLE DO call sp_insert();
Query OK, 0 rows affected (0.001 sec)

MariaDB [testdb]> select now();
+---------------------+
| now()               |
+---------------------+
| 2020-06-06 18:11:06 |
+---------------------+
1 row in set (0.000 sec)

MariaDB [testdb]> select *from events_list;
+------------+---------------------+
| event_name | event_started       |
+------------+---------------------+
| event_now  | 2020-06-06 18:11:10 |
| event_now  | 2020-06-06 18:11:20 |
| event_now  | 2020-06-06 18:11:30 |
| event_now  | 2020-06-06 18:11:40 |
+------------+---------------------+
4 rows in set (0.000 sec)

范例：修改事件‘

MariaDB [testdb]> ALTER DEFINER='root'@'localhost' EVENT event_test ON SCHEDULE EVERY 30 SECOND ON COMPLETION PRESERVE ENABLE DO call sp_insert();

#禁用事件
MariaDB [testdb]> alter event testdb.event_test disable;
MariaDB [testdb]> show events\G

#启用事件
MariaDB [testdb]> alter event testdb.event_test enable;
Query OK, 0 rows affected (0.000 sec)
MariaDB [testdb]> show events\G

#修改事件名称
MariaDB [testdb]> alter event testdb.event_test rename to event_test2;
Query OK, 0 rows affected (0.001 sec)
MariaDB [testdb]> show events\G