What are the different types of SQL triggers?

What are the types of sql triggers? Specific code examples are needed.

In SQL databases, a trigger is a special type of stored procedure that can be automatically executed when a specific event occurs in the database. Triggers are often used to implement data integrity and business logic constraints. SQL triggers can be automatically triggered when data is inserted, updated, or deleted to perform a series of defined operations.

SQL triggers can be divided into the following types:

1. Insert trigger (INSERT Trigger): triggered when a new record is inserted into the table. The following is a sample code for an insert trigger:

CREATE TRIGGER insert_trigger
AFTER INSERT ON table_name
FOR EACH ROW 
BEGIN
    -- 插入触发器的操作代码
    -- 可以在此处进行一些插入数据之后的处理，例如插入新记录后更新另一个表
END

2. Update trigger (UPDATE Trigger): Triggered when an existing record in the table is updated. The following is a sample code for an update trigger:

CREATE TRIGGER update_trigger
AFTER UPDATE ON table_name
FOR EACH ROW 
BEGIN
    -- 更新触发器的操作代码
    -- 可以在此处进行一些记录更新后的处理，例如更新另一个表中的相关记录
END

3. DELETE Trigger: Triggered when a record is deleted from the table. The following is a sample code to delete a trigger:

CREATE TRIGGER delete_trigger
AFTER DELETE ON table_name
FOR EACH ROW 
BEGIN
    -- 删除触发器的操作代码
    -- 可以在此处进行一些删除记录后的处理，例如删除相关联的记录或备份数据等
END

It should be noted that when defining a trigger, you can specify its firing time (AFTER or BEFORE) and the triggered event (INSERT, UPDATE or DELETE ). Use the BEFORE trigger to perform some additional processing before the operation is executed.

In addition to the AFTER trigger in the above example, a BEFORE trigger can also be created. The BEFORE trigger is fired before executing the operation and can be used to verify the validity of the data or perform some preprocessing operations.

In summary, SQL triggers can be used to automatically perform some operations when specific events in the database occur to meet data integrity, business logic constraints and other requirements. According to different needs and scenarios, you can create insert triggers, update triggers, and delete triggers. By defining appropriate triggers, finer control and processing can be achieved during database operations.

The above is an introduction to the types of SQL triggers and corresponding code examples.

The above is the detailed content of What are the different types of SQL triggers?. For more information, please follow other related articles on the PHP Chinese website!