滿足條件的行數

Question

我真的認爲我的問題不是太具體，我只是不知道如何解釋它。

說我有一個表，下面Collumns

team | gameType | date | outcome

我想創建列出有關球隊的一些統計數據的視圖

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

現在我想添加列計算總數

• 這是場聯賽
• 已經在過去的一個月
• 勝
• 損失
• 關係

目的是在數據庫中，沒有任何新的表或列創建一個視圖。

Answer 1

您可以在聚合函數中使用case語句來僅聚合特定事件。

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

總的想法是使用CASE表達式骨料

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

有點更簡單和更可讀內部（至少對我來說）比使用的情況是使用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