Whether MySQL has triggers

mysql Is there a trigger

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mysql There are triggers .MySQL Triggers are a set of SQL Statement set , yes MySQL A powerful tool for managing data in , It is mainly used to protect the data in the table .MySQL Three triggers are supported ：1、INSERT trigger , Is in INSERT Triggers that respond before or after statement execution ;2、UPDATE trigger , Is in UPDATE Triggers that respond before or after statement execution ;3、DELETE trigger , Is in DELETE Triggers that respond before or after statement execution .

The operating environment of this tutorial ：windows7 System 、mysql8 edition 、Dell G3 The computer .

mysql There are triggers .

MySQL The trigger is the same as the stored procedure , Are embedded in MySQL One of the procedures in , Is a set of... Stored in the database directory SQL Statement set , yes MySQL A powerful tool for managing data in . The difference is that executing stored procedures uses CALL Statement to call , And trigger execution doesn't need to use CALL Statement to call , It doesn't need to be started by hand , It is triggered by related operations on the data table 、 Activate to execute . For example, when it comes to student Table operation （INSERT,DELETE or UPDATE） It will be activated to execute .

Triggers are closely related to data tables , It is mainly used to protect the data in the table . Especially when there are multiple tables that are related to each other , Triggers enable different tables to maintain data consistency .

stay MySQL in , Only execute INSERT、UPDATE and DELETE The trigger can only be activated during operation , Other SQL Statement does not activate the trigger .

Advantages and disadvantages of flip flops

The advantages of triggers are as follows ：

• Trigger execution is automatic , Execute immediately after making corresponding modifications to the data of the trigger related table .

• Triggers can be implemented better than FOREIGN KEY constraint 、CHECK Constrain more complex checks and actions .

• Triggers enable cascading changes to table data , To a certain extent, it ensures the integrity of the data .

The disadvantages of triggers are as follows ：

• Business logic implemented with triggers is difficult to locate when problems arise , Especially when multiple triggers are involved , It will make later maintenance difficult .

• Extensive use of triggers can easily cause code structure to be disrupted , Increases the complexity of the program ,

• If the amount of data to be changed is large , The execution efficiency of triggers will be very low .

MySQL There are three kinds of triggers ：

MySQL There are three types of triggers supported ：INSERT trigger 、UPDATE Trigger and DELETE trigger .

1) INSERT trigger

　　 stay INSERT Triggers that respond before or after statement execution .

2) UPDATE trigger

　　 stay UPDATE Triggers that respond before or after statement execution .

3) DELETE trigger

　　 stay DELETE Triggers that respond before or after statement execution .

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