Question

我知道这是一个简单的问题，但我无法在任何地方找到答案。

那是我的表：

city  | CREATE TABLE `city` (
  `ID` int(11) NOT NULL,
  `Name` char(35) NOT NULL DEFAULT '',
  `CountryCode` char(3) NOT NULL DEFAULT '',
  `District` char(20) NOT NULL DEFAULT '',
  `Population` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`ID`),
  KEY `FKcode99` (`CountryCode`),
  CONSTRAINT `FKcode99` FOREIGN KEY (`CountryCode`) REFERENCES `country` (`code`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

问题是：如果要删除某个城市，人口必须为275,000或更少。

我试过

ALTER TABLE `world`.`city` 
RENAME TO  `world`.`DeleteCity` ;
USE `world`;

DELIMITER $$

DROP TRIGGER IF EXISTS world.DeleteCity_ADEL$$
USE `world`$$


CREATE TRIGGER `DeleteCity_ADEL` AFTER DELETE ON `DeleteCity` FOR EACH ROW
IF (OLD.population <= 275000) THEN
    DELETE FROM city WHERE NEW.name=OLD.name;
END IF;
$$
DELIMITER ;

但它不起作用。有谁能够帮我？

Answer 1

我会这样做：

CREATE TRIGGER `DeleteCity_ADEL` BEFORE DELETE ON `DeleteCity` FOR EACH ROW
IF (OLD.population > 275000) THEN
     SIGNAL SQLSTATE '45123'
      SET MESSAGE_TEXT = 'If you want to delete a city, the population must be 275,000 or less.';
END IF;
/

当somone尝试删除包含＆gt;的记录时，此触发器会引发错误。 275,000并向他返回一个明确的解释（错误信息）如果人口少于或等于275,000，则会默默删除记录。

满足条件时删除触发器

1 个答案: