Stephan,
Ah. Well, you answer optimization questions so often that I'd assumed
that you had a hand in it. Is the optimizer all Tom and Bruce's work?
> At least on 7.1 and below, if you have a dummy value that is very
> common
> but doesn't really pass any information (like 'N/A' for example),
> consider
> using NULL instead. The optimizer statistics can often be thrown
> off-kilter by values that are much more common than the real data.
Personally, I cannot reccomend this. There are a number of
normalization problems with using NULL instead of 'N/A' or 0 or another
"no" value. Some database theorists (Fabian Pascal & co.) even propose
the elimination of NULL from the SQL spec on the grounds that it
encourages bad DB design. As such, I have a hard time reccommending any
course that involves adding *more* NULLs to the database, especially for
a marginal query performance gain.
To phrase it another way: Optimization problems cost you seconds. DB
Design and normalization problems cost you *days*.
-Josh Berkus
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