满足条件的行数

Question

我真的认为我的问题不是太具体，我只是不知道如何解释它。

说我有一个表，下面Collumns

team | gameType | date | outcome

我想创建列出有关球队的一些统计数据的视图

SELECT team, count(*) as FROM matches GROUP BY team ORDER BY total DESC

现在我想添加列计算总数

• 这是场联赛
• 已经在过去的一个月
• 胜
• 损失
• 关系

目的是在数据库中，没有任何新的表或列创建一个视图。

Answer 1

您可以在聚合函数中使用case语句来仅聚合特定事件。

SELECT 
    team, 
    count(*) total_matches, 
    count(case when gameType = 'league' then 1 end) league_matches, 
    count(case then date > now() - INTERVAL 30 DAY then 1 end) recent_matches, 
    ... 
FROM matches 
GROUP BY team 

Answer 2

总的想法是使用CASE表达式骨料

SELECT 
    team, 
    count(*) as total, 
    count(CASE WHEN outcome = 'WIN' THEN 1 END) as wins, 
    count(CASE WHEN outcome = 'DRAW' THEN 1 END) as draw, 
    count(CASE WHEN outcome = 'LOSE' THEN 1 END) as losses, 
    count(CASE WHEN gametype = 'League' THEN 1 END) as leaguegames, 
    count(CASE WHEN DATE_SUB(CURDATE(), INTERVAL 1 MONTH) < dateTHEN 1 END) as lastmonth 
FROM matches 
GROUP BY team 
ORDER BY total DESC 

Answer 3

有点更简单和更可读内部（至少对我来说）比使用的情况是使用OR：

SELECT 
    team, 
    count(*) as total, 
    count(outcome = 'WIN' OR NULL) as wins, 
    count(outcome = 'DRAW' OR NULL) as draw, 
    ... 
FROM matches 
GROUP BY team