MySQLの上位5つの値を合計する

これを試してください：

SELECT driver, SUM(`position`)
FROM (SELECT driver, race, season, `position`, 
             IF(@lastDriver=(@lastDriver:=driver), @auto:[email protected]+1, @auto:=1) indx 
      FROM results, (SELECT @lastDriver:=0, @auto:=1) A 
      ORDER BY driver, `position`) AS A  
WHERE indx <= 5 
GROUP BY driver ;