MySQL - Why can't I add a foreign key here? - mysql

Question

I'm not sure why I'm not able to add a particular foreign key here. These tables were generated via MySQL Workbench, and based on the MySQL documentation and on searching for other similar problems / solutions, I think everything is in order...yet I can't add one foreign key in particular:
inspection_statuses.inspection_id needs to reference inspection_responses.tpa_result
What am I missing / overlooking?
This is the statement I'm trying to use to add the new foreign key:
ALTER TABLE `vipsouth_app`.`inspection_statuses`
ADD CONSTRAINT `inspection_statuses_ibfk_3`
FOREIGN KEY (`inspection_id`)
REFERENCES `vipsouth_app`.`inspection_responses` (`tpa_result`)
ON DELETE NO ACTION
ON UPDATE NO ACTION;
And that produces this error:
Operation failed: There was an error while applying the SQL script to the database.
ERROR 1005: Can't create table vipsouth_app.#sql-1f48_7 (errno: 150 "Foreign key constraint is incorrectly formed")
CREATE TABLE `inspection_responses` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`inspection_request_id` int(10) unsigned NOT NULL,
`tpa_result` varchar(10) CHARACTER SET utf8 NOT NULL,
`created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
`created_by` int(10) unsigned NOT NULL DEFAULT '0',
`updated_at` timestamp NULL DEFAULT NULL,
`updated_by` int(10) unsigned DEFAULT NULL,
`deleted_at` timestamp NULL DEFAULT NULL,
`deleted_by` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id_UNIQUE` (`id`),
UNIQUE KEY `tpa_result_UNIQUE` (`tpa_result`),
KEY `inspection_responses_ibfk_1_idx` (`inspection_request_id`),
CONSTRAINT `inspection_responses_ibfk_1` FOREIGN KEY (`inspection_request_id`) REFERENCES `inspection_requests` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `inspection_statuses` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`inspection_request_id` int(10) unsigned NOT NULL,
`inspection_response_id` int(10) unsigned NOT NULL,
`tpa_code` varchar(4) COLLATE utf8_unicode_ci NOT NULL,
`user_id` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
`password` varchar(100) COLLATE utf8_unicode_ci NOT NULL,
`inspection_id` varchar(10) COLLATE utf8_unicode_ci NOT NULL,
`status` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,
`note` varchar(1000) COLLATE utf8_unicode_ci DEFAULT NULL,
`url` varchar(1024) COLLATE utf8_unicode_ci DEFAULT NULL,
`created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
`created_by` int(10) unsigned NOT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
`updated_by` int(10) unsigned DEFAULT NULL,
`deleted_at` timestamp NULL DEFAULT NULL,
`deleted_by` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id_UNIQUE` (`id`),
KEY `inspection_statuses_ibfk_1_idx` (`inspection_request_id`),
KEY `inspection_statuses_ibfk_2_idx` (`inspection_response_id`),
CONSTRAINT `inspection_statuses_ibfk_1` FOREIGN KEY (`inspection_request_id`) REFERENCES `inspection_requests` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `inspection_statuses_ibfk_2` FOREIGN KEY (`inspection_response_id`) REFERENCES `inspection_responses` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

Answer 1

The data types and constraints defined on both the columns should be exactly the same. Except for a foreign key can be NULLable.
This should do it for you. I did not get any error.
SET foreign_key_checks = 0;
CREATE TABLE `inspection_responses` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`inspection_request_id` int(10) unsigned NOT NULL,
`tpa_result` varchar(10) CHARACTER SET utf8 NOT NULL,
`created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
`created_by` int(10) unsigned NOT NULL DEFAULT '0',
`updated_at` timestamp NULL DEFAULT NULL,
`updated_by` int(10) unsigned DEFAULT NULL,
`deleted_at` timestamp NULL DEFAULT NULL,
`deleted_by` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id_UNIQUE` (`id`),
UNIQUE KEY `tpa_result_UNIQUE` (`tpa_result`),
KEY `inspection_responses_ibfk_1_idx` (`inspection_request_id`),
CONSTRAINT `inspection_responses_ibfk_1` FOREIGN KEY (`inspection_request_id`) REFERENCES `inspection_requests` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
CREATE TABLE `inspection_statuses` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`inspection_request_id` int(10) unsigned NOT NULL,
`inspection_response_id` int(10) unsigned NOT NULL,
`tpa_code` varchar(4) COLLATE utf8_unicode_ci NOT NULL,
`user_id` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
`password` varchar(100) COLLATE utf8_unicode_ci NOT NULL,
`inspection_id` varchar(10) COLLATE utf8_unicode_ci NOT NULL,
`status` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,
`note` varchar(1000) COLLATE utf8_unicode_ci DEFAULT NULL,
`url` varchar(1024) COLLATE utf8_unicode_ci DEFAULT NULL,
`created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
`created_by` int(10) unsigned NOT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
`updated_by` int(10) unsigned DEFAULT NULL,
`deleted_at` timestamp NULL DEFAULT NULL,
`deleted_by` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id_UNIQUE` (`id`),
KEY `inspection_statuses_ibfk_1_idx` (`inspection_request_id`),
KEY `inspection_statuses_ibfk_2_idx` (`inspection_response_id`),
CONSTRAINT `inspection_statuses_ibfk_1` FOREIGN KEY (`inspection_request_id`) REFERENCES `inspection_requests` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `inspection_statuses_ibfk_2` FOREIGN KEY (`inspection_response_id`) REFERENCES `inspection_responses` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
SET foreign_key_checks = 1;