You're reusing $sth for different SQL statements at the same time. Don't do that, use different variables, e.g.

$sth=$dbh->prepare("SELECT name,address_number from many_address      
                    WHERE name=?
                    AND number=?
                    AND street=? ");
...
$sth_update=$dbh->prepare("UPDATE many_address
                        SET name=NULL,
                        date_loaded=NULL
                        WHERE name=?
                        AND number=?
                        AND street=? ");
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rdfield