MySQL DELETE語句加入，HAVING和GROUP BY

Question

我有一個項目表和另一個報告。每個報告都有一個外鍵鏈接到正在報告的項目。

我試圖刪除這個查詢中顯示的所有項目：

SELECT items.id, title, SUM(weight) AS total_weight, SUM(weight)*10/views AS score 
FROM items, reports 
WHERE items.id = reports.item_id 
GROUP BY items.id 
HAVING score >= 50; 

嘗試這樣的事：

DELETE items 
FROM (SELECT items.id, title, SUM(weight) AS total_weight, SUM(weight)*10/views AS score 
    FROM items, reports 
    WHERE items.id = reports.item_id 
    GROUP BY items.id 
    HAVING score >= 50) 
AS T; 

給我此錯誤消息：

ERROR 1109 (42S02): Unknown table 'items' in MULTI DELETE 

Answer 1

在MySQL中，您必須小心子查詢。我認爲以下工作：

DELETE FROM items 
WHERE id IN (select * 
      from (SELECT items.id 
        FROM items join reports 
         on items.id = reports.item_id 
        GROUP BY items.id 
        HAVING SUM(weight)*10/views >= 50 
       ) 
      ) 

它使技巧編譯器通過使用額外的子查詢接受查詢。我還修復了您的join語法。

以下，雖然，改寫查詢轉換爲更通用的語法，使用一個相關子查詢：

delete from items 
where exists (select r.item_id 
       from reports r 
       where r.item_id = items.item_id 
       group by r.item_id 
       having SUM(r.weight)*10/items.views >= 50 
      ) 

這是猜測，weight和views在前面來自reports. Otherwise, you need to put the items`別名來代替。

Answer 2

DELETE FROM items 
WHERE 
    id IN (
    SELECT 
     items.id 
    FROM items, reports 
    WHERE items.id = reports.item_id 
    GROUP BY items.id 
    HAVING SUM(weight)*10/views >= 50) 

Answer 3

我相信你的delete聲明是錯誤的。它應該是delete from tablename where [condition]。

DELETE FROM items 
    WHERE 
     id IN (
     Select T.id from (SELECT items.id, title, SUM(weight) AS total_weight, SUM(weight)*10/views AS score 
FROM items, reports 
WHERE items.id = reports.item_id 
GROUP BY items.id 
HAVING score >= 50) T) 

Answer 4

試試這個：

DELETE FROM items 
WHERE id IN (SELECT id 
      FROM (SELECT i.id itemId, (SUM(weight) * 10/views) score 
        FROM items i INNER JOIN reports r ON i.id = r.item_id 
        GROUP BY itemId HAVING score >= 50 
       ) AS A 
      );