MySQL的子查詢優化

Question

我有是非常緩慢運行查詢：

SELECT * 
FROM games 
WHERE games.platform =13 
AND games.id NOT 
IN (SELECT game_id 
FROM collections 
WHERE collections.user_id =1) 

我試圖把它改寫爲左加入，但它返回0結果：

SELECT * 
FROM games 
LEFT JOIN collections ON collections.game_id = games.id 
WHERE collections.game_id IS NULL AND collections.user_id = 1 AND games.platform = 13 
ORDER BY games.name ASC 

莫非有人指出我的錯誤在這裏？

Answer 1

SELECT games.* 
FROM games 
     LEFT JOIN collections 
     ON collections.user_id = 1 
      AND collections.game_id = games.id 
WHERE games.platform = 13 
     AND collections.game_id IS NULL 
ORDER BY games.name ASC 

你需要對指標

• （games.id，平臺名稱）
• （collections.user_id，collections.game_id）