delete trigger when condition is met - mysql

Question

I know it is a simple question but i am not finding the answer anywhere.
That's my 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 |
The question is: If you want to delete a city, the population must be 275,000 or less.
I tried
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 ;
but it doesn't work. Can anybody help me?

Answer 1

I would do it in this way:
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;
/
This trigger raises an error when somone is trying to delete a record with population > 275,000 and returns a clear explanation (error message) to him.
If population is less or equal than 275,000, the record is silently deleted.