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Message Posted: Mon, 26 Sep 2005 @ 11:03:24 GMT


     
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Subj:   Re: The use of ID Columns
 
From:   Dieter Noeth

Naveen Ram Prasanna Kambhoji wrote:

  How far is it beneficial to define an Identity Column as PI in DWH Applications.  


In theory a PK (value and definition) should never change, but in reality it does. If you use a dumb artifical PK (doesn't have to be a sequence) you'll probably never encounter that problem.

But this is about Primary *Key* not Primary *Index*, you should always chosse a PI based on access/joins/distribution.

Btw, in other DBMSes this might be a good idea, because they don't like to join on multiple columns or varchars...


  I heard that joins to ID columns almost always require row distributions.  


If the sequence is the PI then not.


  Why is it so?  


Because it's a rumour and rumours tend to be wrong :-)


  Also what if I want to add more constant values for a multivalued compressed column.  


     create new table -> insert/select -> drop old table -> rename

That's the only way, you'll need twice the perm space (old + new) and enough spool (even if PI is the same and it's a "ins new sel * from old")


Dieter



     
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