How to use triggers and events in MySQL

MySQL is a commonly used relational database management system. Its powerful functions and flexible usage make it the first choice for many developers and enterprises. In MySQL, triggers and events are two important concepts that can implement functions such as data monitoring, data integrity protection, and data synchronization. This article will introduce the use of triggers and events in MySQL.

1. Triggers

1. Overview of triggers

A trigger is a special stored procedure in MySQL that is associated with a table and Automatically trigger predefined actions when adding, deleting or modifying tables. Triggers are divided into three categories: BEFORE triggers, AFTER triggers and INSTEAD OF triggers. The BEFORE trigger fires before the operation is performed, the AFTER trigger fires after the operation is performed, and the INSTEAD OF trigger replaces the original operation before the operation is performed. Through triggers, we can automatically complete some operations when data changes, such as updating related tables, recording logs, sending notifications, etc.

2. Create a trigger

To create a trigger, you need to use the CREATE TRIGGER statement. The syntax is as follows:

CREATE TRIGGER trigger_name
BEFORE/AFTER/INSTEAD OF insert/update/delete
ON table_name
FOR EACH ROW
trigger_body

Among them, trigger_name is the name of the trigger, insert/update/delete is the triggering time, table_name is the name of the table to which the trigger belongs, and trigger_body is the specific logic of the trigger. In trigger_body, you can use NEW to refer to the newly inserted value and OLD to refer to the old value.

3. Example

The following is an example. When a new record is inserted into the table student, a log record is automatically inserted into the table log:

CREATE TABLE student (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(100),
age INT
);

CREATE TABLE log (
id INT PRIMARY KEY AUTO_INCREMENT ,
action VARCHAR(100),
timestamp TIMESTAMP
);

DELIMITER //
CREATE TRIGGER insert_log AFTER INSERT
ON student FOR EACH ROW
BEGIN
INSERT INTO log (action, timestamp) VALUES ('insert', NOW());
END //

When inserting a new record, the trigger will automatically perform the operation of inserting the log. Each inserted action adds a log record, including action type and timestamp.

2. Event

1. Event Overview

Event is a scheduled task in MySQL. It can be executed at a specified time point or periodically. trigger. Through events, we can execute specified SQL statements, stored procedures or call system commands on time. Events can be used in scenarios such as regular backup of data, cleaning of expired data, automatic statistics of data, etc.

2. Creating events

Creating events requires the use of the CREATE EVENT statement. The syntax is as follows:

CREATE EVENT event_name
ON SCHEDULE schedule
[DO sql_statements]
[COMPLETION NOT PRESERVE]
[ENABLE/DISABLE]

Among them, event_name is the event name, schedule is the time expression that triggers the event, sql_statements is the SQL statement or stored procedure call to be executed when the event is triggered, COMPLETION and ENABLE/DISABLE are optional parameters, used to define whether the event retains the completion status and is enabled or disabled respectively. Disable events.

3. Example

The following is an example to perform a backup database operation every morning:

CREATE EVENT backup_event
ON SCHEDULE EVERY 1 DAY
STARTS '2022-01-01 00:00:00'
DO
BEGIN

-- 执行备份操作

END;

Event backup_event defines an event that is executed once a day, from The specified start time becomes effective. When the event is triggered, the SQL operations between BEGIN and END will be executed.

Summary:

Through triggers and events, we can implement some advanced data operations and management functions in MySQL. Triggers can automatically trigger related operations when data changes, and events can perform specific tasks regularly. Their usage is simple and flexible, allowing us to better utilize the powerful functions of MySQL and improve development efficiency and data security.

Through the introduction of this article, I believe that readers have a certain understanding of how to use triggers and events in MySQL, and can use them flexibly in actual development to achieve more efficient database management.

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