Triggers in MySQL

What is a Trigger?

Example: Auto Log

DELIMITER //
CREATE TRIGGER after_student_insert
AFTER INSERT ON students
FOR EACH ROW
BEGIN
    INSERT INTO logs(message)
    VALUES(CONCAT('New student: ', NEW.name));
END //
DELIMITER ;

NEW and OLD

• NEW.column = the new value (INSERT/UPDATE).
• OLD.column = the old value (UPDATE/DELETE).

Summary

• A trigger runs automatically on INSERT/UPDATE/DELETE.
• Use NEW/OLD to access changed values; great for logging and validation.

Trigger क्या है?

Example: Auto Log

DELIMITER //
CREATE TRIGGER after_student_insert
AFTER INSERT ON students
FOR EACH ROW
BEGIN
    INSERT INTO logs(message)
    VALUES(CONCAT('New student: ', NEW.name));
END //
DELIMITER ;

NEW और OLD

• NEW.column = नई value (INSERT/UPDATE)।
• OLD.column = पुरानी value (UPDATE/DELETE)।

सारांश

• Trigger INSERT/UPDATE/DELETE पर अपने आप चलता है।
• बदली values के लिए NEW/OLD use करें; logging और validation के लिए बढ़िया।