Re: [GUSDEV] PK constraints for version tables

[Deborah P. <pi...@pc...>]

You mean drop the uniqueness constraint for the original 
PK+modification_date? 

Steve Fischer wrote:

> 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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