錯誤＃1242子查詢在更新時返回多於一行

Question

這是我以前的question。我無法解決問題。我更新我的代碼，並間接使用GROUP BY。但同樣的問題表明。子查詢返回重複值。其實我做了一個觸發器，因此，我認爲，如果顯示的觸發，這將是清楚明白

-- 
-- Triggers `product_purchases` 
-- 
DROP TRIGGER IF EXISTS `change_stock_when_purchases`; 
DELIMITER // 
CREATE TRIGGER `change_stock_when_purchases` AFTER INSERT ON `product_purchases` 
FOR EACH ROW BEGIN 
    DECLARE X INTEGER; 
    SET X = (SELECT product_size FROM product_stock WHERE product_id = NEW.product_id); 
    IF NEW.product_size =X THEN 
    UPDATE 
     product_stock as S1 
     INNER JOIN 
     (
     SELECT 
      S.product_stock_id,I.quantity 
     FROM 
      product_stock AS S 
     INNER JOIN 
      product_purchase_item AS I 
     ON 
      S.product_id=I.product_id AND S.product_size=I.product_size 
     INNER JOIN 
      product_purchases AS P 
     ON 
      I.product_purchase_item_id=P.product_purchase_item_id 
     WHERE 
      P.product_purchase_id=NEW.product_purchase_id 
     GROUP BY 
      S.product_stock_id 
     ) 
     AS M 
    ON 
     S1.product_stock_id=M.product_stock_id 
    SET 
     S1.product_size_quantity=S1.product_size_quantity+M.quantity; 
    ELSE 
    INSERT INTO 
     product_stock (product_id,product_size,product_size_quantity) 
     SELECT 
      product_id,product_size, quantity 
     FROM 
      product_purchase_item 
     WHERE 
      product_purchase_item_id=NEW.product_purchase_item_id; 
    END IF; 
END 
// 
DELIMITER ; 

問題顯示，當它在你的代碼上product_stock

Answer 1

最可疑的子查詢更新相同product_id S」不同product_size是這一個：

SET X = (SELECT product_size FROM product_stock WHERE product_id = NEW.product_id); 

你有product_stock表中有重複嗎？這是很容易確定：

select product_id 
from product_stock 
group by product_id 
having count(*) > 1; 

如果你這樣做，你可以選擇其中一個作爲：

SET X = (SELECT product_size FROM product_stock WHERE product_id = NEW.product_id limit 1);