根据另一列的计算创建MYSQL触发器以更新列

Question

I have this table

id     price     qty     points

How can I create a trigger so that whenever I update the column price, the column points will be updated based on the calculation of price DIV 10 DIV qty?

I have tried but it does not work and it doesn't update the column points.

delimiter $$
drop trigger if exists cart_update_rewards$$
create trigger cart_update_rewards
after update on cart
for each row 
begin
SELECT `price` DIV 10 DIV `quantity` as points FROM `cart`;
end$$ 

Answer 1

If you want to assign the value to a column in cart , use a "before update" trigger and assign the value in new :

delimiter $$
drop trigger if exists cart_update_rewards$$
create trigger cart_update_rewards
before update on cart
for each row 
begin
    set new.points = new.price DIV 10 DIV new.quantity ;
end$$ 

Answer 2

I have resolved it with help from @GordonLinoff.

DELIMITER //
CREATE TRIGGER trigger_name
BEFORE UPDATE
ON cart FOR EACH ROW
BEGIN
-- trigger code
set new.`reward_points` = new.cart_price DIV 1;
END; // 
DELIMITER ;