How to model optional self dependence in mySQL?

Question

我正在尝试在mySQL中对可选的自相关性进行建模，例如，一门课程可能具有一个或多个先决条件，而这些前提是同一张表中的其他课程。

Answer 1

Have a separate table which lists the course's prerequisites:

create table class_prerequisite (
   classID int not null,
   prerequisiteClass int not null,
   required bit not null default false,
   primary key (classID, prerequisiteClass)
);

where classID and prerequisiteClass are foreign keys pointing back at your classes table. The 'required' field would signal if it's a mandatory or optional prereq.