The first time you encounter something, you're probably going to
make some mistakes. There's a post going around tonight about how
someone forgot to put an index on some database thing and wound up
doing full table scans (or something like that). The rub is that
instead of just being slow, it also cost a fair amount of money
because this crazy vendor system charged by the row or
somesuch. So, by scanning the whole table, they touched all of
those rows, and oh hey, massive amounts of money just set ablaze!
The usual venues are discussing it, and I get the impression some
people have the wrong approach to this. I want to describe a truly
bad database schema I encountered, and then tell you a little about
what it did to the system performance.