Short question since I don’t know how to search for this. Can I “re-update” the same row? For example, I have a field that stores the sub-total of a payment, and given my business constraints I can update that value. Can I update the total of the same row with just a trigger? Thank you beforehand!
By the way I’m using Oracle and PL/SQL.
Business rules: I have the following. There’s a table that stores will pays data, another table that stores the monthly fees to be paid, and another one that stores the possible discounts. One will pay can only be discounted once, and the will pay stores the subtotal and the total. So, what I’m doing is… “when the discount information is being updated, after it’s committed, update the total value and the values of the fees”.
You can’t update the table your trigger is firing against, you’ll get an ORA-04091 mutating table error. You can update values in the row itself, using the
:NEWsyntax, as long as it’s a ‘before’ trigger.I’m unclear what you mean about the subtotal though; it sounds like you have a running total field on the table; if thats based on other records on the same table (e.g. you have multiple records for the same order, and you want an inserted record to have the sum of all the previous ones). If that is the case then you can’t do that either, as you’d hit the same ORA-04901.
If you’re updating a row then you could adjust a field, by setting for example
:NEW.subtotal := :OLD.subtotal - :OLD.value + :NEW.value, but not sure what the benefit of that field would be.It would be helpful to see what your business logic is and how it fits in with the insert/update, and what you want the trigger to do. Often with something like this you really want to be using a wrapper procedure around the insert/update, rather than a trigger, but it’s a bit vague at present.
For the subtotal to remain accurate, I’d probably avoid trying to maintain it all, and instead use a view which has an analytic function calculating it for you. Much less hassle, in my experience.