### Database Schema:
CREATE TABLE prof (
	prof_id	INTEGER	NULL	PRIMARY KEY,
	gender	TEXT	NULL,
	first_name	TEXT	NULL,
	last_name	TEXT	NULL,
	email	TEXT	NULL,
	popularity	INTEGER	NULL,
	teachingability	INTEGER	NULL,
	graduate_from	TEXT	NULL
);

CREATE TABLE RA (
	student_id	INTEGER	NULL	PRIMARY KEY,
	capability	INTEGER	NULL,
	prof_id	INTEGER	NULL	PRIMARY KEY,
	salary	TEXT	NULL,
	foreign key (student_id) references student (student_id),
	foreign key (prof_id) references prof (prof_id)
);

CREATE TABLE student (
	student_id	INTEGER	NULL	PRIMARY KEY,
	f_name	TEXT	NULL,
	l_name	TEXT	NULL,
	phone_number	TEXT	NULL,
	email	TEXT	NULL,
	intelligence	INTEGER	NULL,
	gpa	REAL	NULL,
	type	TEXT	NULL
);

CREATE TABLE registration (
	course_id	INTEGER	NULL	PRIMARY KEY,
	student_id	INTEGER	NULL	PRIMARY KEY,
	grade	TEXT	NULL,
	sat	INTEGER	NULL,
	foreign key (student_id) references student (student_id),
	foreign key (course_id) references course (course_id)
);

CREATE TABLE course (
	course_id	INTEGER	NULL	PRIMARY KEY,
	name	TEXT	NULL,
	credit	INTEGER	NULL,
	diff	INTEGER	NULL
);

### User's Query:
Give the grade score for Rik Unsworth in "Computer Network".

### Extra Knowledge:
Academic grades awarded for participation in a course are A, B, C, D and F where Grade 'A' means excellent, Grade 'B' means good, Grade 'C' means fair, Grade 'D' means poorly pass, if grade is null or empty, it means that this student fails to pass this course in which grade = NULL;
SELECT CASE grade WHEN 'A' THEN 4 WHEN 'B' THEN 3 WHEN 'C' THEN 2 ELSE 1 END AS result FROM registration WHERE student_id IN ( SELECT student_id FROM student WHERE f_name = 'Rik' AND l_name = 'Unsworth' AND course_id IN ( SELECT course_id FROM course WHERE name = 'Computer Network' ) )