> I guess it depends on what you're using it for -- disk space 
> is cheap and
> abundant anymore, I can see some advantages of having it 
> computed only once
> rather than X times, where X is the number of SELECTs as that 
> could get
> costly on really high traffic servers.. Costly not so much for simple
> computations like that but more complex ones.

Once and for all forget the argument in database technology, that disk space 
is cheap in regard to $/Mb. That is not the question. The issue is:
        1. amout of rows you can cache
        2. number of rows you can read from disk per second
             (note that it is not pages/sec)
        3. how many rows you can sort in memory

In the above sence disk space is one of the most expensive things in a
database system. Saving disk space where possible will gain you drastic
performance advantages.

Andreas

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