Question

我想做这样的事情：

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来使用另一个表的元组更新表。

Answer 1

正如in the manual所解释的那样，在定义过程/触发器/等时。在其正文中使用;来分隔命令，您需要定义一个备用分隔符，以便将CREATE命令解释为单个语句。

使用UPDATE的结果SELECT，就像您描述的那样，您可以执行以下任何操作：

将SELECT的结果保存在您在UPDATE中使用的变量中：

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

只需使用子查询（只要它不引用您正在更新的表）：

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

或者只是加入表格：

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

使用子句编写使用另一个表的属性更新表的查询

1 个答案: