Can not add foreign key in mySQL [duplicate] - mysql

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This question already has answers here:
MySQL Error 1215: Cannot add foreign key constraint
(29 answers)
Is storing a delimited list in a database column really that bad?
(10 answers)
Closed 2 years ago.
I want to add foreign key like this
and this is my table user_idea
CREATE TABLE IF NOT EXISTS `user_idea` (
`idea_id` int(5) NOT NULL AUTO_INCREMENT,
`user_id` varchar(30) DEFAULT NULL,
`title` varchar(40) DEFAULT NULL,
`innovators` varchar(30) DEFAULT NULL,
`idea_categories` varchar(30) DEFAULT NULL,
`status` int(5) DEFAULT NULL,
`description` varchar(50) DEFAULT NULL,
PRIMARY KEY (`idea_id`),
KEY `innovators` (`innovators`),
KEY `idea_categories` (`idea_categories`),
KEY `user_id` (`user_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=8 ;
--
-- Dumping data untuk tabel `user_idea`
--
INSERT INTO `user_idea` (`idea_id`, `user_id`, `title`, `innovators`, `idea_categories`, `status`, `description`) VALUES
(1, 'jack', 'Video Annotations', 'jack', '1;2', 1, 'Video Annotations Description'),
(2, 'jack', 'Optimize waterfall model', 'jack;jackson', '3', 0, 'Optimize waterfall model Description'),
(3, 'jackson', 'Automation', 'jackson', '1', 1, 'Automation Description'),
(4, 'jackson', 'Design Patterns', 'jackson', '1', 0, 'Design Patterns Description'),
(5, 'alice', 'Identify Video Objects', 'alice;jack', '2', 1, 'Identify Video Objects Description'),
(6, 'bob', 'Tin Can LMS', 'bob', '1', 1, 'Tin Can LMS Description'),
(7, 'bob', 'Text Summarization', 'bob', '2;3', 0, 'Text Summarization Description');
--
-- Ketidakleluasaan untuk tabel pelimpahan (Dumped Tables)
--
--
-- Ketidakleluasaan untuk tabel `user_idea`
--
ALTER TABLE `user_idea`
ADD CONSTRAINT `user_id` FOREIGN KEY (`user_id`) REFERENCES `user_info` (`id`);
my table idea_category
enter image description here
CREATE TABLE IF NOT EXISTS `idea_categories` (
`category_id` int(5) NOT NULL AUTO_INCREMENT,
`category_name` varchar(50) DEFAULT NULL,
PRIMARY KEY (`category_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;
INSERT INTO `idea_categories` (`category_id`, `category_name`) VALUES
(1, 'Project Lifecycle'),
(2, 'Video'),
(3, 'Language Analysis');
My table user_info:
enter image description here
CREATE TABLE IF NOT EXISTS `user_info` (
`id` varchar(30) NOT NULL,
`full_name` varchar(30) DEFAULT NULL,
`dep_id` int(5) DEFAULT NULL,
`point` int(5) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `dep_id` (`dep_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
INSERT INTO `user_info` (`id`, `full_name`, `dep_id`, `point`) VALUES
('alice', 'Alice W', 2, 1),
('bob', 'Bob S.', 2, 2),
('jack', 'JACK D.', 2, 2),
('jackson', 'M.S.Jackson', 3, 3);
but I got an error cannot add foreign key? Please help