Explain please.

MySql

Show a listing of courses with their prerequisite courses. The results should show the course information for both the course and the prerequisite.

create table course (course_id numeric(8,0), title varchar(50), dept_name varchar(20), credits numeric(2,0) check (credits > 0), primary key (course_id), foreign key (dept_name) references department (dept_name) on delete set null );

create table instructor (ID numeric(5,0), name varchar(20) not null, dept_name varchar(20), salary numeric(8,2) check (salary > 29000), primary key (ID), foreign key (dept_name) references department (dept_name) on delete set null );

create table section (course_id numeric(8,0), sec_id numeric(8,0), semester varchar(6) check (semester in ('Fall', 'Winter', 'Spring', 'Summer')), year numeric(4,0) check (year > 1701 and year < 2100), building varchar(15), room_number numeric(7,0), time_slot_id varchar(4), primary key (course_id, sec_id, semester, year), foreign key (course_id) references course (course_id) on delete cascade, foreign key (building, room_number) references classroom (building, room_number) on delete set null );

create table student (ID numeric(5,0), name varchar(20) not null, dept_name varchar(20), tot_cred numeric(3,0) check (tot_cred >= 0), primary key (ID), foreign key (dept_name) references department (dept_name) on delete set null );

create table takes (ID numeric(5,0), course_id numeric(8,0), sec_id numeric(8,0), semester varchar(6), year numeric(4,0), grade varchar(2), primary key (ID, course_id, sec_id, semester, year), foreign key (course_id, sec_id, semester, year) references section (course_id, sec_id, semester, year) on delete cascade, foreign key (ID) references student (ID) on delete cascade );

create table prereq (course_id numeric(8,0), prereq_id numeric(8,0), primary key (course_id, prereq_id), foreign key (course_id) references course (course_id) on delete cascade, foreign key (prereq_id) references course (course_id) );