my @flds = ( qw/foo bar status/ );
my @vals = @param{@flds};
my $valstr = join( ",", ("?") x @flds );

if ( $param{timestamp} ) {
    push @flds, "timestamp";
    $valstr .= ",NOW()";
}
my $sql = "insert into mytable (" . join( ",", @flds ) . ") values ($valstr)";
my $sth = $dbh->prepare( $sql );
$sth->execute( @vals );