计算满足条件的行

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。

假设我有一个包含以下列的表

team | gameType | date | outcome

我想创建一个列出团队统计信息的视图

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

现在我想添加计算总数的列

• 这是联赛
• 已过去一个月
• 胜利
• 损失
• 关系

目的是在数据库中创建一个视图，而不是任何新的表或列。

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

一般的想法是在聚合

中使用CASE表达式

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

比使用CASE更简单，更易读（至少对我来说）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