What is a Trigger ???

What is  A trigger ?


Trigger is a Mysql script which evokes on different events

before insert
after insert
before update
after update
before delete
after delete

Trigger Syntax

CREATE TRIGGER triggerName BEFORE/AFTER  INSERT/UPDATE/DELETE ON Table 

Example 

mysql> CREATE TABLE account (acct_num INT, amount DECIMAL(10,2));

mysql> CREATE TRIGGER sumofinsertion  BEFORE INSERT ON account
    -> FOR EACH ROW SET @sum = @sum + NEW.amount;

Now when you insert data in account the trigger evokes

BEFORE INSERT means the trigger will execute before the insert action

Let insert some data

mysql> SET @sum = 0;
mysql> INSERT INTO account VALUES(1,25.05),(2,837.50),(3,-123.00);
mysql> SELECT @sum AS 'Total amount inserted';

+-----------------------+
| Total amount inserted |
+-----------------------+
| 739.55               |
+-----------------------+

Similarly can be set for AFTER and BEFORE of INSERT / UPDATE / DELETE

You can Drop Trigger using syntax




DROP TRIGGER 
sumofinsertion 

;



Thanks

Cheers