SQL子查詢聚合錯誤

Question

我有一個記分牌，顯示基於大多數平均得分的當前排名。

我和6位朋友每晚打幾回合。

我們跟蹤： Playername（playerid） 點

輪（多少回合玩法） 平均點（點/輪）（積累輪所有點的總和）這工作，但如果玩家在記分牌上升或下降以及平均得分有多少，我想添加一個計算。

這是我的代碼：

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是前年一輪tournamentid。

但是它沒有正確計算上一輪的平均值，而是取最後一輪的平均值。

結果：

，你可以在這裏看到的avg_last是錯誤的。這裏練成例如其中數字是從哪裏來的：

任何線索如何正確的代碼？嘗試過OVER（），但不支持MariaDB。

Answer 1

您需要使用相關子查詢來獲取該行玩家的平均值。變化：

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

到：

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