my $dbpass = $sth->fetch;
($UIDholder, $LNholder) = @{$dbpass};
...

##</code><code>##

my $dbpass = $sth->fetch
   or die("Bad data. XXX not found\n");
$sth->fetch
   and die("Bad data. Multiple XXX in table YYY\n");
($UIDholder, $LNholder) = @{$dbpass};
...