How to update related table MYSQL? - mysql

Question

There are two tables: orders, orders_history.
orders
________
id | status
orders_history
id | order_id | status | user_id
The orders_history contains history of all user's actions. At the same time orders.status contains the last status from orders_history.status.
I make these queries in transation:
transaction start
insert into orders_history...
$status = select status from order_history order by id desc limit 1;
update orders set status = $status where orders.id = id
My question is:
Should I use transaction and is it properly way to do that?
What if several transactions try to insert, update orders_history for the same order_id.

Answer 1

As suggested in the comments above you could use a trigger to update the orders table -
DELIMITER $$
CREATE TRIGGER `update_order_status` AFTER INSERT ON `orders_history`
FOR EACH ROW
UPDATE `orders` SET `status` = NEW.status WHERE id = NEW.order_id;
$$
DELIMITER ;
The better option would be to not store the redundant status in orders and just query for most recent status in orders_history.
SELECT orders.id, (SELECT status FROM orders_history oh WHERE orders.id = oh.order_id ORDER BY id DESC LIMIT 1) AS status
FROM orders

Answer 2

The design pattern I might use in this case is...
Table 1: History -- this is an audit trail of everything that has gone on. (Think: All the checks written and deposits made to a checking account.)
Table 2: Current -- this is the current status of the information. (Think, current account balance, status, etc.)
Whenever something happens (eg, a check clears):
START TRANSACTION;
INSERT INTO History ...;
UPDATE Current ...;
COMMIT;
In the case of a checking account, something different is needed if your account is overdrawn, so let's make the transaction more complex:
START TRANSACTION;
SELECT balance FROM Current WHERE acct = 123 FOR UPDATE;
if would be overdrawn then
email user
UPDATE Current SET status = 'overdrawn' acct = 123;
...
else
INSERT INTO History ...;
UPDATE Current ...;
endif
COMMIT;
I prefer to put the "business logic" clearly in one place, not hidden in a Trigger. (I might use a Trigger for monitoring or logging, but not for the main purpose of the tables.)