2. 1. An event is an object that is triggered by the
passage of time.
2. MySQL Events were added in MYSQL 5.1.6
3. It’s an alternative to Scheduled Tasks and Cron
Jobs
4. We can schedule events to run either once or
at a recurring interval when you know your
server traffic will be low
What is MySQL Events?
3. Advantages
1. Cross Platform Scheduler
2. No applications Needed
3. It is directly written on Mysql Server
Uses:
1. Events can be used to create backups
2. Processing stale Records
3. We can use them whenever there is a database
update or cleanup required at regular interval.
4.
5. Starting the Event Scheduler
The MySQL event scheduler is a process that runs in the
background and constantly looks for events to execute.
To start the Event scheduler:
SET GLOBAL event_scheduler = ON;
Likewise, to turn all events off you would use:
SET GLOBAL event_scheduler = OFF;
7. Working with Events
It can only perform actions for which the MySQL user that
created the event has privileges to perform
(select * from mysql.user)
Event names are restricted to a length of 64 characters
Events cannot be created, altered, or dropped by another
event.
Unique Event name
8. Create Event Syntax
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}
9. 1. First, you specify the event name after the CREATE
EVENT clause. The event name must be unique within a
database schema.
2. Second, you put a schedule after the ON SCHEDULE clause. If
the event is a one-time event, you use the syntax: AT
timestamp [+ INTERVAL]. If the event is a recurring event, you
use the EVERY clause: EVERY interval STARTS timestamp
[+INTERVAL] ENDS timestamp [+INTERVAL].
3. For “two minutes and ten seconds” can be expressed as +
INTERVAL '2:10' MINUTE_SECOND.
For “three weeks and two days from now” can be expressed
as AT CURRENT_TIMESTAMP + INTERVAL 3 WEEK + INTERVAL 2
DAY
10. 4. Once an event has expired, it is immediately dropped. You
can override this behavior by specifying ON COMPLETION
PRESERVE. Using ON COMPLETION NOT PRESERVE merely
makes the default nonpersistent behavior explicit
5. Place the SQL statements after the DO keyword. It is
important to notice that you can call a stored procedure
inside the body of the event. In case you have compound
SQL statements, you can wrap them in a BEGIN END block.
11. YSLOW DEMO
CREATE EVENT myevent
ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 HOUR
DO
BEGIN
UPDATE mytable SET mycol = mycol + 1;
END |
DELIMITER ;
This event will run once, one hour from the time it was
created
The BEGIN and END statements surround one or multiple
queries which will be executed at the specified time
12. CREATE EVENT e_daily
ON SCHEDULE EVERY 1 DAY
STARTS CURRENT_TIMESTAMP
ENDS CURRENT_TIMESTAMP + INTERVAL 1 YEAR
COMMENT 'Saves total number of sessions then clears the table
each day'
DO
BEGIN
INSERT INTO site_activity.totals (time, total)
SELECT CURRENT_TIMESTAMP, COUNT(*) FROM
site_activity.sessions;
DELETE FROM site_activity.sessions;
END
13. Updating Events
If you want to change an existing event’s behavior rather than deleting it
and recreating it, you can use ALTER EVENT.
For example,
To change the schedule of the previous event to run every month,
starting at some date in the future at 1 o’clock in the morning, you would
use the following:
ALTER EVENT myevent
ON SCHEDULE EVERY 1 MONTH
STARTS '2015-09-30 01:00:00'
