Please remove the COMMIT and give a feedback ;)

Edit
Please change your execute with this one :)

$sth18->execute($userName) or die "Couldn't execute statement: " . $st
+h18->errstr;
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Execute returns a true value if it succeeds and a false value otherwise, so we abort if for some reason the execution fails.

Another important thing is that Rows method is database-driver specific, so it might not work in other drivers, or it might work differently in other drivers.