On Sep 8, 2005, at 5:20 PM, Ted Unangst wrote:
Robert Simpson wrote:
Lets take the October sales further. Lets say if there were any
sales in October, that you had to subtract $100 from the total sales
for October to account for ... lets say "shipping costs".
SELECT SUM(amt) - 100 from sales where month = 'october'
If there were no sales, under your query plan, I'd still have been in
the hole $100.
This is vastly oversimplified in order to show that "0" does not
always answer the question and can cascade into an even worse
scenario.
I would think "SELECT SUM(amt)" means "How much did I sell?" or "What
was my income?", and a better query here would be "SELECT SUM(amt) -
SUM(costs)". Just because there were no sales doesn't mean that the
profit (or loss) is indeterminate. If your boss asked you "How much
did you make in October?" the answer is not "I can't tell."
oh yes, it is the correct answer. "I can't tell because I don't have
the data." Therein lies the problem... if we contrive concrete
examples, we can go both ways -- the way of NULL or the way of 0. The
fact is, NULL is the absence of data. Hence, I can't tell is a valid
answer.
--
Puneet Kishor
