When I first started doing DBI stuff, I made the mistake of thinking, "I thought out this table design carefully, so I'm never going to add or change any fields." So I hardcoded the fields:

my $q=$dbh->query("INSERT INTO foo VALUES (?,?,?,?,?);
$q->execute($bar, $baz, $qx, $qux, $quux);
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Hah. Don't ever do that. You end up tracking down every single query in your code and fixing it. Multiple times.