算術與MySQL的[optmization]

Question

在下面的查詢在不同的表中的列：

SELECT 
    (SELECT nick FROM nicks n WHERE n.pid=p.id LIMIT 1 ORDER BY id DESC) as nick 
    , (
      (
      (SELECT COUNT(*) FROM kills k WHERE k.pid = p.id) 
      + 
      (SELECT COUNT(*) FROM votos v WHERE v.pid = p.id) 
      ) 
      - (SELECT COUNT(*) FROM deaths d WHERE d.pid = p.id) 
) as score 
    , (SELECT COUNT(*) FROM kills k WHERE k.pid = p.id) as kills 
    , (SELECT COUNT(*) FROM deaths d WHERE d.pid = p.id) as deaths 
    , (SELECT COUNT(*) FROM headshots h WHERE h.pid = p.id) as headshots 
    , (SELECT COUNT(*) FROM votos v WHERE v.pid = p.id) as reputation 
FROM players p 
WHERE p.uuid='STEAM_x:x:xxxxxx' 
GROUP BY kills 

此查詢工作正常...但我認爲存在着一個更好的方式來做到這一點。 任何人都可以幫助我優化此查詢嗎？

Answer 1

下面是編寫查詢稍微更好的辦法：

SELECT p.*, (kills + reputation - deaths) as score 
FROM (SELECT (SELECT nick FROM nicks n WHERE n.pid = p.id ORDER BY id DESC LIMIT 1 
      ) as nick, 
      (SELECT COUNT(*) FROM kills k WHERE k.pid = p.id) as kills, 
      (SELECT COUNT(*) FROM deaths d WHERE d.pid = p.id) as deaths, 
      (SELECT COUNT(*) FROM headshots h WHERE h.pid = p.id) as headshots, 
      (SELECT COUNT(*) FROM votos v WHERE v.pid = p.id) as reputation 
     FROM players p 
     WHERE p.uuid = 'STEAM_x:x:xxxxxx' 
    ) p 
GROUP BY kills; 

注：我不明白什麼GROUP BY在做什麼。您只是按一列進行彙總，所以其餘列的值有，並且不確定值。也許你打算ORDER BY。

我猜測在group by之前實現子查詢的開銷略小於其他子查詢。但是你的版本可能具有非常可比的性能。

對於任一版本，您希望達到以下指標：

• players(uuid)
• kills(pid)
• deaths(pid)
• headshots(pid)
• votos(pid)