MySQL查询和显示统计信息

Question

表：

statistics (columns: id, wins, draws, losses, round1, round2, round3)
matches (columns: id, home_id,away_id,home1, away1, home2, away2, home3, away3)

我想获得每场比赛的平均得分。基本上它是： 总得分/比赛

我可以获得总分： ROUND1 + round2 + round3

总共玩游戏：

COUNT(id) FROM matches

如何获得我想要的结果？

SELECT
COUNT(matches.id) AS totalgames,
SUM(statistics.round1+round2+round3/COUNT(matches.id))

FROM matches, statistics

这显然不起作用......