That's not a general rule for preferring bags to sets, it's an exception to the rule.

In any event, I think it's also a mistake. You want two aggregate functions, SUM and COUNT. If you're iterating over duplicate results like that, you've made a mistake. Ignoring that most (all?) SQL implementations support an AVG operator, you could always do this:

SELECT SUM(age) / COUNT(age) AS average_age FROM table

So with all due respect, even your special case doesn't seem to me to be applicable.

Of course, that's brings up a related issue:

SELECT SUM(customer_id) / COUNT(customer_id) FROM customers

That's clearly nonsense but it's quite legal. If SQL followed the relational model it wouldn't even compile.

Cheers,
Ovid

New address of my CGI Course.

In reply to Re^6: (OT) Why SQL Sucks (with a little Perl to fix it) by Ovid
in thread (OT) Why SQL Sucks (with a little Perl to fix it) by Ovid

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