L' Eomot Inversé (3/20/2013)

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demonfox (3/20/2013)

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Danny Ocean (3/20/2013)

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Good question.

In real life scenario, we need to take care of cascade option.

I prefer not to have delete cascade on design .. to let the error display when the constraint doesn't allow it..

well, delete cascase could be a better option for delete based on performance , but with proper indexing , I guess, basic deletes shouldn't be too intensive process ..

and , it keeps of mistakes off the track 🙂 that's what constraints are for ...

No, constraints are to ensure that the schema enforces its own integrity and that you don't have to write code to enforce it. It means that you can't make mistakes that would lead to an invalid state of the schema, not that you can't make mistakes at all.

Avoiding ON DELETE CASCADE is usually a mistake; it requires code to be written to do something the system could do for you - and that code costs development time and testing time and integration time and may contain bugs (for example sometimes deleting some rows in the referring table that it shouldn't delete, or sometimes not deleting all the referring rows that it should delete, or deleting all the referring rows but omitting deletion of the referred row) which can have highly undesirable results. If you are worried about bugs that delete the wrong order, will increasing the code size and complexity prevent those bugs or do nothing to stop them while introducing potentilly more bugs?

If on the other hand you are worried about someone carelessly doing a manual delete on an order row that shouldn't be deleted, why do your procedures allow manual deletes? If you need manual deletes, is forcing people to use a much more error prone manual process (find the detail rows and delete them first, then delete the order row) instead of a simple manual process (just delete the order row and let the system take care of the rest) going to make them more likely or less likely to make mistakes? If you don't want certain things to be deleted all, why does anyone have delete permissions on them in the first place? Is it possible that in eschewing use of ON UPDATE CASCADE you are trying to fix operational issues involving people, which is usually (always, as far as Iknow) not something you can do in a computer program?