SUM( MAX(..) )

function kills($MID){
	global $oMysql;	
	$_ = "	SELECT
				MAX(NID) as kills
			FROM
				`tbl`
			WHERE
				MID = '". $MID ."'
			GROUP BY
				UID
		 ";
	$_ = $oMysql->query($_);	
	for($iKills=0;$a=mysql_fetch_assoc($_);$iKills += $a['kills']);
	return $iKills;
}

function kills($MID){
	global $oMysql;	
	$_ = "	SELECT
				MAX(NID) as kills
			FROM
				`tbl`
			WHERE
				MID = '". $MID ."'
			GROUP BY
				UID
		 ";
	$_ = $oMysql->query($_);	
	for($iKills=0;$a=mysql_fetch_assoc($_);$iKills += $a['kills']);
	return $iKills;
}