Copy and pasted (near enough from PHP admin but still does not like it..
$conn->query("UPDATE `pmuryxvf_shoes`.`Job` SET `shoe_id` = NULL WHERE `Job`.`job_id` =".$jobid.";");
What im attempting to do is set a row to NULL. Can you see the issue. If I place another value were the NULL is its fine.
One last thing - this row is a foreign key but a NULL value can be updated via PHPMyadmin
The error appears to be telling you that your data model defines shoe_id as a NOT NULL column. You cannot, therefore, set it to be NULL.
You could modify the table definition to allow NULL values
ALTER TABLE pmuryxvf_shoes
MODIFY( shoe_id INT NULL )