paul c wrote:
> Jan Hidders wrote:
>>
>> Another small thing is updating primary keys. If a primary key has
>> accidentally been entered wrong and you want to fix that with an
>> update then it is usually not possible to simply update it, and the
>> problem gets even worse if it is also refered to by foreign keys. In
>> an ER model this is a non-problem.
>
> like a few other people (i suspect we are a minority), i think of
> 'update' as a sugaring or shortcut. ignoring transaction or concurrency
> issues, is there any logical difference between 'update' and the
> combination of 'delete-insert'?
Splitting the update in a delete and an insert makes the situation even
more complex. Assume a relation S that has a foreign key to the primary
key of R. For an update to the PK of a tuple in R it is easy to see what
it means to cascade that update to S. If you split the update in a
delete and an insert this is not so simple because on the delete you
would have to either (1) delete the corresponding tuples in S or (2)
nullify their foreign keys, so if you then follow with only the insert
you will have lost information. So, yes, there is a logical difference.
Received on Thu Jul 07 2005 - 15:36:05 CDT
