MySQL: Getting current row ID in update - mysql

Question

So I'm working on this trigger that updates an account balance as soon as one of the transaction types logged on it is changed. Here is the query:
BEGIN
IF (OLD.debit != NEW.debit) THEN
UPDATE account,
(SELECT accountid,
sum(accountentry.amountaccountentry) AS total
FROM accountentry
WHERE accountentry.typeid = NEW.idaccounttype
AND accountentry.accountid = account.idaccount
GROUP BY accountentry.accountid) AS s
SET account.balanceaccount = IF(NEW.debit = 1, IF(s.total IS NOT NULL, balanceaccount - s.total * 2, balanceaccount), IF(s.total IS NOT NULL, balanceaccount + s.total * 2, balanceaccount));
END IF;
END
Now, this query does work if I remove the "AND accountentry.accountid = account.idaccount" part. Since I'm in some kind of "sub query", how would I go about retrieving the id of the account I'm currently updating?
Thanks a lot :)

Answer 1

I agree with the goal of keeping redundant data out of the database but I also understand that this is not always practical. In this case, retrieving the balance by aggregating the transactions should be very low cost if appropriate indices are in place. I do not know the details of your specific scenario but, at the very least, you should be very cautious when introducing redundant data. It will almost certainly become inconsistent at some point.
Having this update in a trigger, as opposed to plainly visible in a transaction in your application's code, is a likely source of hard to track bugs in the future.
You have not included enough information (CREATE TABLE statements, sample data, desired outcome) in your question for me to answer with confidence but I will have a go.
Your update query appears to be attempting to handle the scenario where the transaction type for one entry is being changed from debit to credit or vice versa but it does not allow for the amountaccountentry changing at the same time. I do not understand why you are using GROUP BY and SUM when you are only dealing with a change to one accountentry. Surely you could use -
BEGIN
IF (OLD.debit != NEW.debit AND OLD.amountaccountentry = NEW.amountaccountentry) THEN
UPDATE account
SET account.balanceaccount = IF(NEW.debit = 1, IF(NEW.amountaccountentry IS NOT NULL, balanceaccount - (NEW.amountaccountentry * 2), balanceaccount), IF(NEW.amountaccountentry IS NOT NULL, balanceaccount + (NEW.amountaccountentry * 2), balanceaccount))
WHERE idaccount = NEW.accountid;
END IF;
END
or if amountaccountentry could change at the same time -
BEGIN
IF (OLD.debit != NEW.debit) THEN
UPDATE account
SET account.balanceaccount = IF(NEW.debit = 1, IF(NEW.amountaccountentry IS NOT NULL, balanceaccount - (OLD.amountaccountentry + NEW.amountaccountentry), balanceaccount), IF(NEW.amountaccountentry IS NOT NULL, balanceaccount + (OLD.amountaccountentry + NEW.amountaccountentry), balanceaccount))
WHERE idaccount = NEW.accountid;
END IF;
END
If I have completely misunderstood your issue, please update your question with the additional details mentioned above.