How to create a column that will be the product of two others?

Question

MySQL

I tried to do this for a long time, it turns out only to withdraw a, I can’t assign

Answer 1

Why add something when you can count?

CREATE TABLE `test`.`test_table` (
  `id` INT NOT NULL,
  `price` INT NULL,
  `count` INT NULL,
  PRIMARY KEY (`id`));

SELECT id, price, count, (price * count) as total FROM test.test_table;

In addition, there is a good rule to create a historical table for the store. Where the order is stored, products and discounts applied at the moment.
And accordingly, you insert there only at the time of placing an order.