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What are MySQL triggers and how to use them?

The MySQL trigger is a database object that is associated with a table. It will be activated when a defined action is executed for the table. Then, the trigger can be executed when you run one of the following MySQL statements on the table:?INSERT,?UPDATE?and?DELETE and it can be invoked before or after the event.?

In addition, you can find detailed explanation of the trigger functionality and syntax?in this article.

In fact, the main requirement for running such MySQL Triggers is having MySQL?SUPERUSER?privileges.

Such privileges can be granted on the?VPS?and Dedicated Servers. Granting?SUPERUSER?MySQL privileges to a user hosted on a Shared Server is not possible due to our server setup.

Here is an example of a MySQL trigger:

1. Firstly, we will create the table for which the trigger will be set via SSH.

mysql>?CREATE?TABLE?people?(age?INT,?name?varchar(150));

2. Next we will define the trigger. It will be executed before every INSERT statement for the people table.

mysql> delimiter //mysql> CREATE TRIGGER agecheck BEFORE INSERT ON people FOR?EACH?ROW?IF?NEW.age?<?0?THEN?SET?NEW.age?=?0;?END?IF;//?Query?OK,?0?rows?affected?(0.00?sec)mysql>?delimiter?;

3. Then, we will insert two records to check the trigger functionality.

mysql>?INSERT?INTO?people?VALUES?(-20,?‘Adam’),?(30,?‘Mark’);Query?OK,?2?rows?affected?(0.00?sec)Records:?2?Duplicates:?0?Warnings:?0

4. Lastly, we will check the result.

mysql>?SELECT *?FROM?people;+――-+――-+|?age?|?name?|+――-+――-+|?0?|?Adam?||?30?|?Mark?|+――-+――-+2?rows?in?set?(0.00?sec)

We hope this article helped you to learn about what are MySQL triggers and how to use them. For more articles, kindly visit our Knowledge Base.

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