Question

I have a trigger in MySQL table. Table has about 20 columns.

DELIMITER $$
CREATE
DEFINER=`root`@`localhost`
TRIGGER `completion_date_update`
BEFORE UPDATE ON `orders`
FOR EACH ROW
BEGIN
  IF NEW.`order_status` = 'COMPLETED' THEN
    SET NEW.`completion_date` = NOW();
  END IF;

  IF NEW.`order_status` != 'COMPLETED' THEN
    SET NEW.`completion_date` = NULL;
  END IF;
END$$

What I want is this trigger to update completion_date column only when column order_status is updated. If any other column is updated this trigger should not do anything.
What is actually happening is this trigger is updating completion_date upon any column update.

Can anyone explain to me why does this happen and what did I do wrong?

order_status column is NOT NULL and has possible values as below:

enum('NEW','OPEN','COMPLETED','CANCELLED','REPLACED')

Default is 'NEW'

Thanks

Answer 1

you should also compare if order_status has been changed and that the new value is COMPLETED

IF (NEW.order_status <> OLD.order_status) AND (NEW.order_status = 'COMPLETED') THEN 
    SET NEW.completion_date = NOW();
END IF;

and you can remove the other IF below.