Do what the error message says. Add

    $sth->finish;
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before you disconnect.

That error is DBI telling you that you still have an open statement handle when you're disconnecting. It's not a fatal error because DBI can always close them up for you. But an open statement handle at the time of disconnecting could be a sign of problems, and not closing the statement handles could cause you problems. So just call finish on the statement handle.