更新前我的SQL触发器

Question

I apologise if this question has been asked a million times before!

So I am trying to create a trigger on a table when an employee is assigned a task the pick_date is updated to show this. It only should update the date field if its null. The order number, employee and order_pick_date are all on the same table.

I have the following trigger but I can't seem to get it to run.

CREATE TRIGGER pickDate BEFORE UPDATE
ON order_master
FOR EACH ROW BEGIN
UPDATE order_master SET NEW.order_pick_date = IFNULL(SYSDATE(),) WHERE  order_master.order_no = old.order_no
END;

Answer 1

A before update trigger is fine. You just do not want to do an update . Simply set the value on the new record:

CREATE TRIGGER pickDate BEFORE UPDATE
ON order_master
FOR EACH ROW BEGIN
    SET NEW.order_pick_date = COALESCE(old.order_pick_date, now()) ;
END;

There are some other issues (such as getdate() being SQL Server syntax), but I think this is what you intend.