How to create trigger for broken cars using IF statement - mysql

Question

I want to create a trigger that will not allow to rent a car if it is currently being repaired. Im quite new in triggers... could anyone shed some light on this aspect of triggers? My assumptions would be that it would something like...
DELIMITER $$
CREATE TRIGGER `inspections_const` BEFORE UPDATE ON `inspections` FOR EACH ROW BEGIN
SET NEW.booking_id = IF.repair_complete = 'No'
THEN 'Allow booking'
ELSE 'Do not allow'
END;
END
$$
DELIMITER ;
Table is
CREATE TABLE `inspections` (
`inspection_id` int(10) NOT NULL,
`inspection_date` date NOT NULL,
`vehicle_id` int(10) NOT NULL,
`problem` varchar(50) NOT NULL,
`repair_complete` enum('Yes','No') NOT NULL,
`mechanic_id` int(10) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `bookings` (
`booking_id` int(50) NOT NULL,
`booking_date` date NOT NULL,
`start_date` date NOT NULL,
`end_date` date NOT NULL,
`invoice_no` int(10) NOT NULL,
`chauffeur_id` int(10) DEFAULT NULL,
`vehicle_id` int(10) NOT NULL,
`customer_id` int(50) NOT NULL,
`chauffeur_req` enum('Yes','No') NOT NULL,
`special_instructions` varchar(255) NOT NULL,
`TheDuration` varchar(10) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Answer 1

I didn't tested it so it might have a missing condition or something like that. But it should help you on the correct path
Query
DELIMITER $$
CREATE TRIGGER `check_repair` BEFORE INSERT ON `bookings` FOR EACH ROW BEGIN
# We need to save the "count"
DECLARE inspections_count INT DEFAULT 0;
# Check if where is a repair going which matches the vehicle_id
SELECT
1 INTO inspections_count # store the "count" into the variable.
FROM inspections
WHERE
inspections.vehicle_id = NEW.vehicle_id
AND
repair_complete = 'No'
ORDER BY
inspections.start_date DESC
LIMIT 1;
# if there is a "count" stop the insert.
IF inspections_count = 0 THEN
SIGNAL SQLSTATE '45000'
SET MESSAGE_TEXT = 'vehicle is in repair';
END IF;
END
$$
DELIMITER ;