MySQL Events are tasks that run on a predefined schedule. As a result, MySQL events are sometimes referred to as scheduled events.
MySQL Events are also called named objects that contain at least one SQL explanation. They are saved in the database and run at regular intervals.
MySQL Event Scheduler is in charge of managing the scheduling and execution of Events. They are analogous to cronjobs in Linux or task schedulers in Windows.
For example, you could schedule an event that optimizes all tables in the database to run every Sunday at 1:00 a.m.
MySQL Events are also referred to as “temporal triggers” because they are triggered by time rather than DML events, as normal triggers are.
This blog will teach you about the MySQL event scheduler and how to use it to automate repetitive database tasks.
Table of Contents
What is MySQL?
MySQL is a dependable Database Management System (DBMS) that employs Structured Query Language (SQL) to perform data-related operations. Its well-known version provides an open-source platform to which you can easily gain access and carry out your Data Management responsibilities.
However, the superior MySQL variations, which can be tailored to meet your specific requirements, are available for a monthly fee.
Companies nowadays rely on the MySQL platform to provide a scalable and dependable solution to their business needs.
MySQL‘s ease of use has given it an advantage over competing DBMS systems like Microsoft SQL Server and Oracle Databases.
Furthermore, you could work seamlessly with MySQL and any programming language used in your industry.
This platform also works seamlessly with Linux, Unix, Windows, and other operating systems.
And depending on your configuration needs, you could use MySQL after downloading it to your local machine or directly from a server.
MySQL is the go-to choice for scalable web applications because it comes standard in the LAMP Stack, which is an Open-Source suite of web applications comprised of Linux, Apache HTTP Server, MySQL, and PHP.
Key Features of MySQL
MySQL is a popular DBMS on the market due to the following features:
- Oracle maintained: It also provides premium MySQL versions that include additional services, proprietary plugins, user support, and extensions.
- An old-pal: MySQL has been around for over 20 years, since its initial release in 1995.
- Updates: MySQL is becoming more robust as a result of frequent updates, which include new features and security enhancements. The most recent version is 8.0.23, which was released on January 18, 2021.
- MVCC (Multi-Version Concurrency Control) Features: MySQL has recently begun to offer MVCC (Multi-Version Concurrency Control) features.
- A Helpful Community: A dedicated community of developers is available to assist with troubleshooting as needed.
- Easy Access: MySQL is a free and open-source relational database management system (RDBMS).
- n- Users: MySQL is widely used by companies such as Google, NASA, Flickr, GitHub, Netflix, Tesla, Twitter, Uber, Wikipedia, YouTube, and Zendesk, to name a few.
What is MySql Event Scheduler?
MySQL Event Scheduler is a background thread that manages the execution of scheduled events. Unless the global variable event_scheduler is set to ON or 1, the Scheduler is in a dormant state.
The MySQL Event Scheduler is MySQL’s replacement for the Cron job. The Event Scheduler has the following advantages:
- It is directly written on the MySQL Server.
- It is platform and application agnostic.
- It can be used whenever there is a need for a regular database update or cleanup.
- It reduces the number of queries that must be compiled.
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Configuration of the MySQL Event Scheduler
The MySQL Event Scheduler state can be set to enable, disable, or turn on the Scheduler.
Run the following command to check the Event Scheduler’s status:
The state of the Event Scheduler is shown by the event_scheduler system variable in the result.
The event_scheduler variable state, in this case, is Waiting on an empty queue, indicating that the Scheduler is active and waiting for an event to trigger it.
Creating a new MySQL Event
We can use the following syntax for creating an event:
The IF NOT EXIST statement makes sure that the event name is not been used before. In place of event_name syntax, we need to specify a unique event name.
Using the ON SCHEDULE we can schedule the event.
You need to enter the SQL statements in place of the event_body syntax after the DO keyword.
MySQL Events execute at a time specified by the user, they are also known as temporal triggers. They should not be confused with MySQL Triggers, which are database objects that are executed in response to specific events.
As a result, to avoid confusion, it is preferable to refer to scheduled tasks as events.
- One Time Event
- Recurring Event
One Time Event
A one-time event is executed once and then deleted automatically.To create a one-time event, specify the timestamp after the ON SCHEDULE statement as follows:
AT timestamp + [INTERVAL interval]
The possible choices of intervals are:
The timestamp must be in the future as a DATETIME or TIMESTAMP value. To specify an exact time, use + INTERVAL, a positive integer, and one of the interval options to add an interval to the timestamp. Please keep in mind that this only applies when using the CURRENT_TIMESTAMP function.
The event occurs two days after it is created, and the task is to delete a table named test.
After execution, events are automatically dropped.
Let us understand more clearly with an example.
- First, we need to create a table named “Demo” using the below command.
- Then we will create an event using the below command.
- Now we will check the Demo table in the data set there is one line that got inserted utilizing the event scheduler since we specify the time as the current timestamp as the scheduled time.
- Now after using the following command to display all the events from the database, the above-created event will not show in that list as it’s a one-time event so it is expired after its execution and the event will automatically drop.
- Now to keep the event after it is expired we can use the ON COMPLETION PRESERVE clause.
- Now using the below command we can check the events list.
A recurring event occurs on a regular basis at a predetermined time. After the ON SCHEDULE statement, use the following syntax to schedule a recurring event:
STARTS timestamp [+ INTERVAL]
ENDS timestamp [+ INTERVAL]
The STARTS keyword specifies when event execution begins, while the ENDS keyword specifies when event execution concludes.
This event causes MySQL to drop table test once each six months, starting immediately.
You can also specify an interval to start the event later.
You can also specify the start time and end time for the event:
This event makes MySQL drop the table named test once every six months for five years, starting five days from now.
All the events stored in the database can be displayed using the following command.
You need to use the ON COMPLETION PRESERVE clause when creating the event to see the one-time events as they are automatically dropped after execution.
Use the ALTER EVENT statement to change an existing event:
The event_name must be an event that already exists. All the statements after ALTER EVENT are optional, depending on what you want to change.
To delete (drop) an event, use the following syntax:
This action permanently deletes the event from the database.
Using the IF EXISTS statement issues a warning if such an event does not exist:
MySQL Event Scheduler Limitations
- Events do not have the ability to return a result set. The output is directed to dev/null, and the event succeeds or fails without informing the user.
- The names of events are not case-sensitive. Two events with the same name but different cases cannot exist.
- There can be two events with the same schedule, but no execution order can be forced.
- An event is always run with definer permissions. The thread executes the event as the user who created it, with all of that user’s privileges.
- The maximum number of recursive calls is max_sp_recursion_depth. Recursivity is disabled if this variable is set to 0, which is the default value.
- Because BEGIN WORK block is treated as the start of the BEGIN END statement, use the START TRANSACTION statement instead.
- Any limitation of stored procedures also applies to events.
Frequently Asked Questions (FAQs)
What is delimiter MySQL?
The delimiter is used when there is a need to define the stored procedure, and function as well as to create triggers. The semicolon is a default delimiter but if you are considering multiple statements, then you need to use different delimiters like $$ or //.
How is Microsoft SQL different from MySQL?
SQL is highly secured and doesn’t allow any kind of database file manipulation while running and while SQL is a query programming language that manages RDBMS MySQL is a relational database management system that uses SQL.
What are the triggers of MySQL?
A trigger is a named data set object that is related to a table, and that enacts when a specific occasion happens for the table. A few purposes for triggers are to perform checks of values to be embedded into a table or to perform computations on values engaged with an update.
You now understand how to automate database management with MySQL Events. Experiment with different statements to see how they affect the events, and combine them with other MySQL features like stored procedures.
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If you have reached here then we presume you liked reading about MySQL Event Scheduler.
Hence, you can also read about working with the Airflow Scheduler if you are working with Apache Airflow to manage multiple workflows in your organization.
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