Re: how is checksum calculated?

Hi Wreck,
many people recommend checksum to detect changes when no other
mechanism is available. To use checksums you must be aware there is
ALWAYS the possibility of a false negative. That is, a row changes but
the checksum is the same. If you can tolerate false negatived by all
means go ahead.

Personally, I prefer to know for sure that all changes have made it to
the DW. And in the DWs I deal with the 'solution' to 'false negatives'
of reloading everything is just not an option......I even wrote my own
delta generation code to deal with these cases for my
clients........and it even understands nulls which are the bane of
detecting changes between tables in relational databases because where
a = b returns false if a or b are null.....because null does not equal
null in set theory though clearly if a field was null yesterday and is
null today it has not changed....

Best Regards

Peter Nolan

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