MySQL中的事件调度器，EVENT，也叫定时任务，类似于Unix crontab或Windows任务调度程序。
EVENT由其名称和所在的schema唯一标识。
EVENT根据计划执行特定操作。操作由SQL语句组成，语句可以是BEGIN…END语句块。EVENT可以是一次性的，也可以是重复性的。一次性EVENT只执行一次，周期性EVENT以固定的间隔重复其操作，并且可以为周期性EVENT指定开始日期和时间、结束日期和时间。（默认情况下，定期EVENT在创建后立即开始，并无限期地继续，直到它被禁用或删除。）
EVENT由一个特殊的事件调度器线程执行，用SHOW PROCESSLIST可以查看。
root@database-one 13:44: [gftest]> show variables like '%scheduler%';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| event_scheduler | OFF |
+-----------------+-------+
1 row in set (0.01 sec)
root@database-one 13:46: [gftest]> show processlist;
+--------+------+----------------------+-----------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+--------+------+----------------------+-----------+---------+------+----------+------------------+
......
+--------+------+----------------------+-----------+---------+------+----------+------------------+
245 rows in set (0.00 sec)
root@database-one 13:46: [gftest]> set global event_scheduler=1;
Query OK, 0 rows affected (0.00 sec)
root@database-one 13:47: [gftest]> show variables like '%scheduler%';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| event_scheduler | ON |
+-----------------+-------+
1 row in set (0.01 sec)
root@database-one 13:47: [gftest]> show processlist;
+--------+-----------------+----------------------+-----------+---------+------+------------------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+--------+-----------------+----------------------+-----------+---------+------+------------------------+------------------+
......
| 121430 | event_scheduler | localhost | NULL | Daemon | 33 | Waiting on empty queue | NULL |
......
+--------+-----------------+----------------------+-----------+---------+------+------------------------+------------------+
246 rows in set (0.01 sec)
可以看到，默认情况下，MySQL的EVENT没有打开，通过设置event_scheduler参数来打开或者关闭EVENT。打开后就会多一个event_scheduler，这个就是事件调度器线程。
除了打开和关闭，还可以禁用，要禁用EVENT，请使用以下两种方法之一：
启动MySQL时用命令行参数
--event-scheduler=DISABLED
在MySQL配置文件中配置参数
event_scheduler=DISABLED
MySQL 5.7中创建EVENT的完整语法如下：
CREATE
[DEFINER = user]
EVENT
[IF NOT EXISTS]
event_name
ON SCHEDULE schedule
[ON COMPLETION [NOT] PRESERVE]
[ENABLE | DISABLE | DISABLE ON SLAVE]
[COMMENT 'string']
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}
详细说明可以参考官网https://dev.mysql.com/doc/refman/5.7/en/create-event.html
我们通过一个实例来验证下。
1）创建一张表。
root@database-one 13:47: [gftest]> create table testevent(id int auto_increment primary key,create_time datetime);
Query OK, 0 rows affected (0.01 sec)
root@database-one 13:50: [gftest]> select * from testevent;
Empty set (0.00 sec)
2）创建一个EVENT，每3秒往表中插一条记录。
root@database-one 13:50: [gftest]> create event insert_date_testevent on schedule every 3 second do
-> insert into testevent(create_time) values(now());
Query OK, 0 rows affected (0.01 sec)
root@database-one 13:53: [gftest]> show events G
*************************** 1. row ***************************
Db: gftest
Name: insert_date_testevent
Definer: root@%
Time zone: +08:00
Type: RECURRING
Execute at: NULL
Interval value: 3
Interval field: SECOND
Starts: 2020-03-26 13:53:10
Ends: NULL
Status: ENABLED
Originator: 1303306
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
1 row in set (0.00 sec)
3）过一会，去表中查询数据。
root@database-one 13:53: [gftest]> select * from testevent;
+----+---------------------+
| id | create_time |
+----+---------------------+
| 1 | 2020-03-26 13:53:10 |
| 2 | 2020-03-26 13:53:13 |
| 3 | 2020-03-26 13:53:16 |
| 4 | 2020-03-26 13:53:19 |
| 5 | 2020-03-26 13:53:22 |
| 6 | 2020-03-26 13:53:25 |
| 7 | 2020-03-26 13:53:28 |
| 8 | 2020-03-26 13:53:31 |
| 9 | 2020-03-26 13:53:34 |
| 10 | 2020-03-26 13:53:37 |
| 11 | 2020-03-26 13:53:40 |
| 12 | 2020-03-26 13:53:43 |
| 13 | 2020-03-26 13:53:46 |
| 14 | 2020-03-26 13:53:49 |
| 15 | 2020-03-26 13:53:52 |
| 16 | 2020-03-26 13:53:55 |
+----+---------------------+
16 rows in set (0.00 sec)
从表里数据可以看到，创建的插数定时任务已经在正常运行了。
EVENT的详细信息除了用show event命令，还可以从mysql.event或information_schema.events中查询，也可以用show create event命令查看。
root@database-one 00:09: [gftest]> select * from mysql.event G
*************************** 1. row ***************************
db: gftest
name: insert_date_testevent
body: insert into testevent(create_time) values(now())
definer: root@%
execute_at: NULL
interval_value: 3
interval_field: SECOND
created: 2020-03-26 13:53:10
modified: 2020-03-26 13:53:10
last_executed: 2020-03-26 16:09:37
starts: 2020-03-26 05:53:10
ends: NULL
status: ENABLED
on_completion: DROP
sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
comment:
originator: 1303306
time_zone: +08:00
character_set_client: utf8
collation_connection: utf8_general_ci
db_collation: utf8_general_ci
body_utf8: insert into testevent(create_time) values(now())
1 row in set (0.00 sec)
root@database-one 00:09: [gftest]> select * from information_schema.events G
*************************** 1. row ***************************
EVENT_CATALOG: def
EVENT_SCHEMA: gftest
EVENT_NAME: insert_date_testevent
DEFINER: root@%
TIME_ZONE: +08:00
EVENT_BODY: SQL
EVENT_DEFINITION: insert into testevent(create_time) values(now())
EVENT_TYPE: RECURRING
EXECUTE_AT: NULL
INTERVAL_VALUE: 3
INTERVAL_FIELD: SECOND
SQL_MODE: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
STARTS: 2020-03-26 13:53:10
ENDS: NULL
STATUS: ENABLED
ON_COMPLETION: NOT PRESERVE
CREATED: 2020-03-26 13:53:10
LAST_ALTERED: 2020-03-26 13:53:10
LAST_EXECUTED: 2020-03-27 00:10:22
EVENT_COMMENT:
ORIGINATOR: 1303306
CHARACTER_SET_CLIENT: utf8
COLLATION_CONNECTION: utf8_general_ci
DATABASE_COLLATION: utf8_general_ci
1 row in set (0.02 sec)
root@database-one 00:10: [gftest]> show create event insert_date_testevent G
*************************** 1. row ***************************
Event: insert_date_testevent
sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
time_zone: +08:00
Create Event: CREATE DEFINER=`root`@`%` EVENT `insert_date_testevent` ON SCHEDULE EVERY 3 SECOND STARTS '2020-03-26 13:53:10' ON COMPLETION NOT PRESERVE ENABLE DO insert into testevent(create_time) values(now())
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
1 row in set (0.00 sec)