我的奇子查詢，需要一個LEFT JOIN改進

Question

下面是一個簡單的SQL轉儲：https://gist.github.com/JREAM/99287d033320b2978728

• 我有一個選擇，抓住用戶的捆綁。
• 然後我做一個foreach循環來將所有關聯的tree_processes附加到該用戶。
• 所以我最終做X查詢：用戶*樹。

把它們放在一起會不會更高效？

• 我想過做一個LEFT JOIN子選擇，但我很難讓它正確。
• 下面我做了一個查詢來選擇SELECT中的正確數據，但是我必須爲所有15行執行此操作，並且它看起來像是浪費內存的TERRIBLE。

這是我的髒Ateempt：

-

SELECT 
      s.id, 
      s.firstname, 
      s.lastname, 
      s.email, 
      (
       SELECT tp.id FROM tree_processes AS tp 
       JOIN tree AS t ON (
        t.id = tp.tree_id 
       ) 
       WHERE subscribers_id = s.id 
       ORDER BY tp.id DESC 
       LIMIT 1 
      ) AS newest_tree_id, 
      # 
      # Don't want to have to do this below for every row 
      (
       SELECT t.type FROM tree_processes AS tp 
       JOIN tree AS t ON (
        t.id = tp.tree_id 
       ) 
       WHERE subscribers_id = s.id 
       ORDER BY tp.id DESC 
       LIMIT 1 
      ) AS tree_type 


    FROM subscribers AS s 
    INNER JOIN scenario_subscriptions AS ss ON (
     ss.subscribers_id = s.id 
    ) 

    WHERE ss.scenarios_id = 1 
    AND ss.completed != 1 
    AND ss.purchased_exit != 1 
    AND deleted != 1 

    GROUP BY s.id 
    LIMIT 0, 100 

這是我LEFT JOIN嘗試，但我遇到麻煩SELECT值

SELECT 
     s.id, 
     s.firstname, 
     s.lastname, 
     s.email, 
     freshness.id, 
     # freshness.subscribers_id < -- Cant get multiples out of the LEFT join 


FROM subscribers AS s 
INNER JOIN scenario_subscriptions AS ss ON (
    ss.subscribers_id = s.id 
) 


LEFT JOIN (SELECT tp.id, tp.subscribers_id AS tp FROM tree_processes AS tp 
      JOIN tree AS t ON (
       t.id = tp.tree_id 
      ) 
      ORDER BY tp.id DESC 
      LIMIT 1) AS freshness 
ON (
    s.id = subscribers_id 
) 

WHERE ss.scenarios_id = 1 
AND ss.completed != 1 
AND ss.purchased_exit != 1 
AND deleted != 1 

GROUP BY s.id 
LIMIT 0, 100 

Answer 1

在LEFT JOIN中，您使用「新鮮」作爲桌面別名。這在你選擇你需要另外說明你想從它的列（s）。由於只需要添加一列（id）：

freshness.id 

到select子句。

你的左連接的ON子句看起來也很狡猾。也許freshness.id = ss.subscribers_id？

歡呼聲 -