How do I get MySQL tables to update each other?

Question

I'm new to programming so please forgive my ignorance. I'm trying to get MySQL tables to update each other. For example: When I insert data into a Primary Key column in one table, it does not appear in it's Foreign Key column in another table.

Does anyone have any advice on this issue?

Thank you!

Additional Information: I used phpMyAdmin to create my tables and then added SQL code to create the Foreign Keys. Example of code is below.

ALTER TABLE CourseSchedule
ADD FOREIGN KEY (CourseId)
REFERENCES Course(CourseId)

Answer 1

I believe what we have here is a slight misunderstanding of the documentation .

For storage engines supporting foreign keys, MySQL rejects any INSERT or UPDATE operation that attempts to create a foreign key value in a child table if there is no a matching candidate key value in the parent table.

When an UPDATE or DELETE operation affects a key value in the parent table that has matching rows in the child table, the result depends on the referential action specified using ON UPDATE and ON DELETE subclauses of the FOREIGN KEY clause. MySQL supports five options regarding the action to be taken, listed here

What your foreign key actually does is to make sure that you cannot insert values into your CourseSchedule table that do not correspond to an entry in the Courses table.

To give you an example, suppose you were to try to enter schedule a python course for every wednesday at 9:00 but you dont' actually have an entry for python in your Courses table. Then mysql will refuse to create that entry. Mysql cannot do the reverse. It doesn't know details about your python course. So it cannot automatically create a entry in the Courses table for you. Similarly, if oyu created an entr in the courses table. Mysql cannot automatically create a CourseSchedule for you because it doesn't know at what time it should be scheduled.