Re: [GUSDEV] PK constraints for version tables

[Steve F. <sfi...@pc...>]

how about just dropping the uniqueness constraint of the modification date?

steve

Chris Sarnowski wrote:

>
> I can't speak for GUS needs in this particular case, but I've had the  
> same issue in other systems. Deborah is correct in that these fields  
> are not right for PK. The question is how important it is to preserve  
> exact order of the changes to the data. If it's not critical you  
> could just drop the PK. If it is (or even if it's not but you believe  
> in the rule "every table must have a PK"), then you should use a  
> surrogate key from a sequence. In practice, at least, the sequence  
> values increase monotonically so changes to a record that occur  
> multiple times with the same modification date can still be ordered  
> correctly.
> I prefer the latter, in general, but I suppose adding a new surrogate  
> key field to all version tables in GUS would be a pretty big deal.
>
> Just my thoughts.
> -Chris Sarnowski
>
> On Oct 21, 2005, at 11:07 AM, Deborah Pinney wrote:
>
>> I suggest that we drop the uniqueness constraint for PKs of version  
>> tables. PKs for these tables consist of the original PK and the  
>> modification date. Rapid computation can result in uniqueness  
>> copnstraint violations that are not remedied by date format  changes. 
>> There doesn't seem to be a purpose in having these  constraints for 
>> any of the version tables and dropping the  constraints would not 
>> result in the loss of information or change  query results. I don't 
>> know if there is implicit indexing on these  keys but I wonder if 
>> this could be handled using explicit indexing.
>
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