What is the difference between pre and post trigger in MySQL?

The main difference between Before and After trigger in MySQL is that Before trigger performs an action before a certain operation is executed on the table while After trigger performs an action after a certain operation is executed on the table.

MySQL is a popular DBMS that allows users to easily retrieve and manage data in relational databases. Stores data in tabular format. The user can perform various operations on the data using Structured Query Language (SQL). Whereas, Trigger is a store program that is automatically executed or fired when some kind of event occurs. The response to the trigger depends on the type of trigger.

Key Areas Covered

1. What is Trigger in MySQL
     – Definition, Functionality
2. What is Before
Trigger in MySQL      – Definition, Functionality
3. What is After Trigger in MySQL?
     – Definition, Functionality
4. What is the difference between pre and post trigger in MySQL?
     – Comparison of key differences

Key terms

After trigger, Before Trigger, MySQL

What is a trigger in MySQL?

A trigger is a set of actions that respond to an operation such as an insert, update, or delete operation on a specific table. The trigger fires when an SQL operation is executed. In addition, triggers can be created using reference constraints and check constraints that allow data integrity rules to be applied. Also, the trigger helps to update other tables. Additionally, it automatically generates or converts values ​​for inserted or updated records or performs tasks such as issuing alerts.

What is before firing in MySQL

Before trigger is a trigger that is executed before an operation like insert, update, delete. The user can write these triggers in multiple cases. They help to verify or modify values ​​before updating or inserting data in the database. It is also possible to execute other non-database operations coded in user-defined functions.

An example of a trigger before the insert operation is as follows.

Create trigger trigger_name

before inserting

   IN table name FOR EACH ROW

START

   – variable declarations

   – trigger code

FINISH;

The trigger_name is used to identify the trigger. Is the name of the trigger to create. The “BEFORE INSERT” statement indicates that the trigger will fire before the insert operation is executed. The table_name indicates the name of the table on which the trigger is created. These triggers will update the new values. The old values ​​in the table will remain the same.

What is After Trigger in MySQL?

After trigger is a trigger that is executed after an operation like insert, update, delete. The user can write these triggers in multiple cases. You can use them to update data in tables. You can also use it to execute non-database operations coded in user-defined functions.

An example of a trigger after the insert operation is as follows.

Create trigger trigger_name

after insert

   IN table name FOR EACH ROW

START

   – variable declarations

   – trigger code

FINISH;

The trigger_name is used to identify the trigger. Is the name of the trigger to create. The “AFTER INSERT” statement indicates that the trigger will fire after the insert operation is executed. The table_name indicates the name of the table on which the trigger is created. These triggers will update the new values. The old values ​​will remain the same.

Difference between pre and post trigger in MySQL

Definition

Before Trigger is a type of trigger that is executed automatically before a certain operation occurs on the table. In contrast, after trigger is a type of trigger that runs automatically after a certain operation occurs on the table. Therefore, these definitions explain the fundamental difference between before and after trigger in MySQL.

Use

Typically the use of Before triggers is to perform validation before accepting data into the table and to check values ​​before removing them from the table. But typically the use of After triggers is to update data in a table due to a change that has occurred. So the main difference between before and after trigger in MySQL is where we use them.

Example

In a banking application, before the trigger helps to check the values ​​before deleting them while after the trigger helps to update the balance in the account table.

conclusion

The main difference between before and after trigger in MySQL is that the before trigger performs an action before a certain operation is executed on the table while the after trigger performs an action after a certain operation is executed on the table.

Reference:

1. “Types of triggers,” IBM Knowledge Center, Available here.
2. “MySQL: BEFORE INSERT Trigger”, Tech on the Net, Available here.
3. “AFTER THE TRIGGER IS INSERTED,” Tech on the Net, Available here.

Courtesy image:

1. “Database-mysql” By RRZEicons – Own work (CC BY-SA 3.0) via Commons Wikimedia