Cannot insert row into table with foreign key field - mysql

Question

I am working on a PHP application that uses a database extensively. My coworker who set up the database, set up the tables to use foreign keys. Here is the statement I am using:
INSERT INTO patients (ethnicity, gender)
VALUES (1, 1);
INSERT INTO sessions (patient_id, submitted, age_in_years, video, annotated)
VALUES (LAST_INSERT_ID(), NOW(), 0, '', FALSE);
The first statement works. However, I get the following error with the second statement.
#1452 - Cannot add or update a child row: a foreign key constraint fails (`<database name>/sessions`, CONSTRAINT `fk_sessions_1` FOREIGN KEY (`patient_id`) REFERENCES `patient` (`id`) ON DELETE CASCADE ON UPDATE CASCADE)
I have confirmed that LAST_INSERT_ID() returns the expected value.
How can I fix this?
Below is how we set up the sessions table
CREATE TABLE IF NOT EXISTS `sessions` (
`id` int(11) NOT NULL auto_increment,
`patient_id` int(11) NOT NULL,
`severity` enum('Minimal Symptoms of Autism Spectrum Disorder','Mild-to-Moderate Symptoms of Autism Spectrum Disorder','Severe Symtoms of Autism Spectrum Disorder') default NULL,
`submitted` datetime default NULL,
`age_in_years` int(11) NOT NULL,
`video` text NOT NULL,
`annotated` tinyint(1) default '0',
PRIMARY KEY (`id`),
KEY `fk_sessions_1` (`patient_id`),
KEY `age_in_years` (`age_in_years`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
ALTER TABLE `sessions`
ADD CONSTRAINT `fk_sessions_1` FOREIGN KEY (`patient_id`) REFERENCES `patient` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;
EDIT: Removed unnecessary details. If you feel you need more, feel free to look at the first version of this post.

Answer 1

It turns out that when my coworker added the foreign key, he had a typo in the table name that the foreign key references.
ALTER TABLE `sessions`
ADD CONSTRAINT `fk_sessions_1` FOREIGN KEY (`patient_id`) REFERENCES `patient` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;
should be
ALTER TABLE `sessions`
ADD CONSTRAINT `fk_sessions_1` FOREIGN KEY (`patient_id`) REFERENCES `patients` (`id`) ON DELETE CASCADE;

Answer 2

The error is telling you exactly what's wrong.
You're attempting to insert a value in sessons.patient_id that does not exist in patients.id. This is how foreign key constraints work by design. Regardless of whether or not the value of LAST_UPDATE_ID() is what you expect, you need to confirm that the value is valid in patients.id.
Example:
patients
---------------
id | name
---------------
1 | john
2 | jane
If you try to insert "3" into sessions.patient_id, you will get the error you see because that id doesn't exist in patients.