满足条件时删除触发器

Question

我知道这是一个简单的问题，但我在任何地方都找不到答案。

那是我的 table:

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：如果要删除一个城市，人口必须在27.5万以下。

我试过了

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。有谁能够帮助我？

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;
/

当某人试图删除人口大于 275,000 的记录并且 returns 向他提供明确的解释（错误消息）时，此触发器会引发错误。
如果人口小于或等于 275,000，记录将被静默删除。

满足条件时删除触发器

delete trigger when condition is met

mysql

triggers

sql-delete