MySQL check ENUM column in another table throughout constraint - mysql

Question

I have two tables:
--
--
--
CREATE TABLE `staff` (
PRIMARY KEY (`staff_id`),
`staff_id` SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NOT NULL,
`staff_type` ENUM('expert', # Perito
'injured' # Danneggiato
) NOT NULL
)ENGINE=InnoDB;
INSERT INTO `x8k1y_staff`
(`staff_id`, `name`, `staff_type`)
VALUES
(1, 'Name surname', 'expert'),
(2, 'John Doe', 'injured');
--
--
--
CREATE TABLE `risk_location` (
PRIMARY KEY (`risk_loc_id`),
`risk_loc_id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
`injured` SMALLINT UNSIGNED NOT NULL,
CONSTRAINT `fk_injured`
FOREIGN KEY (`injured`)
REFERENCES `staff` (`staff_id`)
ON DELETE CASCADE,
)ENGINE=InnoDB;
But I want to raise an MySQL Error if a user tries to insert a staff_id that doesn't have a value of "injured" in staff_type.
For example:
INSERT INTO risk_location (`injured`)
VALUES (1); # <--- Here I want an error, because the `staff_type` of id 1 is `expert`
INSERT INTO risk_location (`injured`)
VALUES (2); # <--- This is ok
Thank you

Answer 1

You can't do that with a constarint
but you can use a trigger
eventually you need a DELIMITER before and after, depending how you add a trigger
CREATE TABLE `staff` (
PRIMARY KEY (`staff_id`),
`staff_id` SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NOT NULL,
`staff_type` ENUM('expert', # Perito
'injured' # Danneggiato
) NOT NULL
)ENGINE=InnoDB;
INSERT INTO `staff`
(`staff_id`, `name`, `staff_type`)
VALUES
(1, 'Name surname', 'expert'),
(2, 'John Doe', 'injured');
CREATE TABLE `risk_location` (
PRIMARY KEY (`risk_loc_id`),
`risk_loc_id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
`injured` SMALLINT UNSIGNED NOT NULL,
CONSTRAINT `fk_injured`
FOREIGN KEY (`injured`)
REFERENCES `staff` (`staff_id`)
ON DELETE CASCADE
)ENGINE=InnoDB;
CREATE TRIGGER before_risk_location_insert
BEFORE INSERT
ON risk_location FOR EACH ROW
BEGIN
DECLARE _staff_type varchar(10);
SELECT staff_type
INTO _staff_type
FROM staff
WHERE staff_id = NEW.injured;
IF _staff_type = 'expert' THEN
signal sqlstate '45000' set message_text = 'user is expert';
END IF;
END
INSERT INTO risk_location (`injured`)
VALUES (1); # <--- Here I want an error, because the `staff_type` of id 1 is `expert`
user is expert
INSERT INTO risk_location (`injured`)
VALUES (2); # <--- This is ok
db<>fiddle here