i neglected to show it properly
have tables A, B, C, D PLUS a few others
A <- B
F
|
v
A <- C <- D
^
|
E
i want to delete from C and cascade any delete to E or F but not if
there are records in D
what i have done is to have ON DELETE CASCADE on C's primary
but force deletes to C through a function that will delete from C only
if there is no records in D
but i would like to believe there is a better way - a way that does not
require that i do all my deletes through a function
cheers
murray
Oliver Elphick wrote:
>
> 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
>
> If the reference from D to C uses ON DELETE RESTRICT (or NO ACTION), that
> should fail and thus cause the original DELETE to fail.
>
> --
> Oliver Elphick [EMAIL PROTECTED]
> Isle of Wight http://www.lfix.co.uk/oliver
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> ========================================
> "For God hath not appointed us to wrath, but to obtain
> salvation by our Lord Jesus Christ, Who died for us,
> that, whether we wake or sleep, we should live
> together with him."
> I Thessalonians 5:9,10
Jan Wieck wrote:
>
> 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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> # Let's break this rule - forgive me. #
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