SQL子查询聚合错误

Question

我有一个记分牌，根据获得的大多数平均分数显示当前排名。

我和6个朋友每晚都会玩几轮。

我们追踪： 玩家名称（playerid） 点（轮次累积的所有点数的总和） 轮次（打了多少轮） 平均积分（积分/轮次）

这样可行，但我想添加一个计算，如果玩家在记分牌中上升或下降以及平均点数。

这是我的代码：

SELECT   t1.playerid as player
                ,SUM(t1.points) AS points
                ,count(t1.playerid) AS rounds
                ,avg(t1.points) as average_points

/* get tournament ID of last round */
                ,(select distinct(tournamentid) from pokermax_scores order by tournamentid desc limit 1,1) as 1_round_ago

/* calculate average points earned one round ago */                
                ,(select avg(points) from pokermax_scores  where tournamentid <= 1_round_ago group by t1.playerid) as avg_last
                ,(avg(t1.points)-(select avg(points) from pokermax_scores  where tournamentid <= 1_round_ago group by t1.playerid)) as gain_loss
FROM pokermax_scores as t1
GROUP BY player
ORDER BY average_points DESC

1_round_ago是最后一轮的巡回赛。

然而，它没有正确计算最后一轮的平均值，而是采用上一轮平均值的平均值。

结果：

正如你在这里看到的那样，avg_last是错误的。这里有数字来自的例子：

有任何线索如何纠正代码？尝试了OVER（）但MariaDB不支持。

Answer 1

您需要使用相关子查询来获取行中玩家的平均值。变化：

(select avg(points) 
from pokermax_scores  
where tournamentid <= 1_round_ago 
group by t1.playerid)

为：

(select avg(points) 
from pokermax_scores t2 
where tournamentid <= 1_round_ago 
and t2.playerid = t1.playerid)