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MariaDB : BEFORE INSERT Trigger

Tutorial by:      Date: 2016-04-19 00:00:52

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This MariaDB tutorial explains how to create a BEFORE INSERT Trigger in MariaDB with syntax and examples.

Description

A BEFORE INSERT Trigger means that MariaDB will fire this trigger before the INSERT operation is executed.

Syntax

The syntax to create a BEFORE INSERT Trigger in MariaDB is:

CREATE TRIGGER trigger_name

BEFORE INSERT

   ON table_name FOR EACH ROW

 

BEGIN

 

   -- variable declarations

 

   -- trigger code

 

END;

Parameters or Arguments

trigger_name

The name of the trigger to create.

BEFORE INSERT

It indicates that the trigger will fire before the INSERT operation is executed.

table_name

The name of the table that the trigger is created on.

Restrictions

  • You can not create a BEFORE trigger on a view.
  • You can update the NEW values.
  • You can not update the OLD values.

Note

  • See also how to create AFTER DELETE, AFTER INSERT, AFTER UPDATE, BEFORE DELETE, and BEFORE UPDATE triggers.
  • See also how to drop a trigger.

Example

Let's look at an example of how to create an BEFORE INSERT trigger using the CREATE TRIGGER statement in MariaDB.

If you had a table created as follows:

CREATE TABLE contacts

( contact_id INT(11) NOT NULL AUTO_INCREMENT,

  last_name VARCHAR(30) NOT NULL,

  first_name VARCHAR(25),

  birthday DATE,

  created_date DATE,

  created_by VARCHAR(30),

  CONSTRAINT contacts_pk PRIMARY KEY (contact_id)

);

We could then use the CREATE TRIGGER statement to create an BEFORE INSERT trigger as follows:

DELIMITER //

 

CREATE TRIGGER contacts_before_insert

BEFORE INSERT

   ON contacts FOR EACH ROW

 

BEGIN

 

   DECLARE vUser varchar(50);

 

   -- Find username of person performing INSERT into table

   SELECT USER() INTO vUser;

 

   -- Update create_date field to current system date

   SET NEW.created_date = SYSDATE();

 

   -- Update created_by field to the username of the person performing the INSERT

   SET NEW.created_by = vUser;

 

END; //

 

DELIMITER ;

 

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