Re: protected ON DELETE CASCADE

Murray Hobbs wrote:
>
> here's my problem
>
> i have tables A, B, C, D
>
> A <- B
> A <- C <- D
>
> i want to maintain integrity so that if A is deleted from then so is
> anything referencing from B and C - no problem ON DELETE CASCADE
>
> but if there are any D's that point back to A (through composite key in
> C) i don't want the delete to go ahead - at all - i want an error
> message and condition

So B and C reference A with ON DELETE CASCADE, while D
references C without it. The default behaviour of a foreign
key constraint is ON DELETE NO ACTION, which confusingly
enough aborts the transaction (it's defined that way in the
SQL standard, don't ask me why they called it NO ACTION).
Thus a deletion from A will cascaded delete from C, but then
the constraint on D will abort the transaction if this
automatic delete from C would orphan a reference from D.

Jan

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