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Question

我想要做这样的事情写使用其他表的属性更新表的查询：

CREATE TRIGGER addwinner AFTER INSERT ON bids 
FOR EACH ROW BEGIN 
IF exists(select * from wins as LT where LT.item_index=NEW.item_index) THEN 

SELECT item_index, MIN(bid_amount) 
FROM update_winnerslist AS a1 
WHERE a1.item_index = NEW.item_index; 
UPDATE wins SET email_id=NEW.emai_id, bid_amount=a1.bid_amount where wins.item_index=a1.item_index; 

END IF; 
END; 

基本上我想要的是通过比较某些属性使用另一个表的元组更新表。

Answer 1

如所解释的in the manual，限定步骤/触发器/等时。在其主体内使用;来分隔命令，则需要定义一个备用分隔符，以便将CREATE命令解释为单个语句。

要UPDATE与SELECT的结果，像你描述的，你可以做任何的：

1. 保存SELECT的一个变量，你再在UPDATE使用结果：

   DELIMITER ;; -- or anything else you like 
   
   CREATE TRIGGER addwinner AFTER INSERT ON bids FOR EACH ROW 
       IF EXISTS (SELECT * FROM wins AS LT WHERE LT.item_index=NEW.item_index) 
       THEN 
       SELECT MIN(bid_amount) INTO @bid_amount 
       FROM update_winnerslist AS a1 
       WHERE a1.item_index = NEW.item_index; 
   
       UPDATE wins 
       SET email_id=NEW.emai_id, bid_amount=@bid_amount 
       WHERE wins.item_index=a1.item_index; 
       END IF;; -- whatever command delimiter you chose above goes here 
   
   DELIMITER ; -- reset to normal 
   

2. 只要使用子查询（只要它没有引用要更新的表）：

   DELIMITER ;; -- or anything else you like 
   
   CREATE TRIGGER addwinner AFTER INSERT ON bids FOR EACH ROW 
       IF EXISTS (SELECT * FROM wins AS LT WHERE LT.item_index=NEW.item_index) 
       THEN 
       UPDATE wins 
       SET wins.email_id=NEW.emai_id, wins.bid_amount=(
        SELECT MIN(bid_amount) 
        FROM update_winnerslist AS a1 
        WHERE a1.item_index = NEW.item_index 
       ) 
       WHERE item_index = NEW.item_index 
       END IF;; -- whatever command delimiter you chose above goes here 
   
   DELIMITER ; -- reset to normal 
   

3. 还是刚刚加入的表：

   DELIMITER ;; -- or anything else you like 
   
   CREATE TRIGGER addwinner AFTER INSERT ON bids FOR EACH ROW 
       IF EXISTS (SELECT * FROM wins AS LT WHERE LT.item_index=NEW.item_index) 
       THEN 
       UPDATE wins JOIN update_winnerslist AS a1 USING (item_index) 
       SET wins.email_id=NEW.emai_id, wins.bid_amount=MIN(a1.bid_amount); 
       WHERE item_index = NEW.item_index 
       END IF;; -- whatever command delimiter you chose above goes here 
   
   DELIMITER ; -- reset to normal