使用COUNT，但仅用于特定值

Question

我有一个表格，里面保存有比赛，我想生成一张表格，显示其中的当前排名。 到目前为止，我的代码如下所示：

SELECT DISTINCT cname, COUNT(cname) AS games, **COUNT(points WHERE points=3) AS wins**, 1, 0, SUM(goalsscored)-SUM(goalsconceded) AS goaldiff, SUM(po$
FROM pmatch
GROUP BY cname
ORDER BY point DESC, goaldiff DESC

我保存了每场比赛以及球队在那场比赛中得到的积分。 因此，我只需要计算每场比赛的胜负，即每支球队获得3分才能赢得胜利，有1分才能赢得平局，而0分则可以输掉局面。

但是，COUNT命令不起作用，因为我希望它起作用。 在粗体部分，您看到我想计算每队获得3分的比赛。 如何正确执行此操作？

提前非常感谢！

Answer 1

使用CASE表达式。

询问

SELECT cname, 
COUNT(cname) AS games, 
SUM(CASE points WHEN 3 THEN 1 ELSE 0 END) AS wins,
SUM(CASE points WHEN 1 THEN 1 ELSE 0 END) AS draws,
SUM(CASE points WHEN 0 THEN 1 ELSE 0 END) AS loses,
SUM(goalsscored)-SUM(goalsconceded) AS goaldiff
FROM pmatch
GROUP BY cname
ORDER BY 3 DESC, 6 DESC;

Answer 2

只需使用CASE ：

SELECT cname, COUNT(cname) AS games, COUNT(case when points=3 then 1 end) AS wins, 1, 0, SUM(goalsscored)-SUM(goalsconceded) AS goaldiff
FROM pmatch
GROUP BY cname
ORDER BY wins DESC,  -- probably
     goaldiff DESC