Re: delete cascade

From: paul c <toledobythesea_at_oohay.ac>
Date: Mon, 16 Apr 2007 22:17:16 GMT
Message-ID: <MBSUh.83937$DE1.76718@pd7urf2no>

Bob Badour wrote:
> paul c wrote:
>

>> Bob Badour wrote:
>>
>>> paul c wrote:
>>>
>>>> I sometimes wonder why the above noun used in place of an adjective 
>>>> is needed.    When the table/relation definition of a line item 
>>>> references an invoice number can it mean anything other than that 
>>>> the line item doesn't exist unless the invoice exists?  Ie., why 
>>>> shouldn't delete always mean so-called "cascade"?
>>>>
>>>> (just trying to keep Marshall interested.)
>>>
>>>
>>>
>>> Because some times it means: "If a line item exists, the invoice must 
>>> also exist."
>>
>>
>>
>> Please forgive my thickness, but doesn't "line item doesn't exist 
>> unless..." (ie., "only if") "...the invoice exists" mean the same?

>
>
> No. One states that deleting the invoice automatically deletes any items
> that exist. The other states that one may not delete an invoice when any
> items exist.

Thanks, that clears up my confusion. Still, it strikes me as more an attitude than a logical interpretation. If I could, I'd rather wonder how to declare a reference from the logical complement of invoices to the complement of items!

p Received on Mon Apr 16 2007 - 17:17:16 CDT