Triger in sql

In simplicity Trigger's are used to perform some database operation if any defined event occurs on a specific table. Trigger call on Insert, Update and delete operation on before/after these event completed. To grab data we have to keyword new and old.
INSERT: new
UPDATE: new/old
DELETE: old

Syntax for creating trigger:
CREATE TRIGGER triger_name
BEFORE | AFTER event ON table_name
BEGIN
...
END;


example:

DELIMITER $$
CREATE TRIGGER updatedata
    AFTER UPDATE ON employees
    FOR EACH ROW
BEGIN
    UPADTE history
    SET old_sal=old.sal where emp_id=old.emp_id;
END$$
DELIMITER ;

DELIMITER $$
CREATE TRIGGER name_add
    BEFORE UPDATE ON employees
    FOR EACH ROW
BEGIN
    SET new.name=concat(new.salut,' ',new.fname,' ',new.lname);
END$$
DELIMITER ;

mysql> delimiter //
mysql> CREATE TRIGGER upd_check BEFORE UPDATE ON account
    -> FOR EACH ROW
    -> BEGIN
    ->     IF NEW.amount < 0 THEN
    ->         SET NEW.amount = 0;
    ->     ELSEIF NEW.amount > 100 THEN
    ->         SET NEW.amount = 100;
    ->     END IF;
    -> END;//
mysql> delimiter ;


sql to see all triggers : SHOW TRIGGERS;
sql to drop trigger: DROP TRIGGER trigger_name;