Database schema:

CREATE TABLE "RA" (
	student_id INTEGER -- example: ['2', '5'],
	capability INTEGER -- example: ['2', '5'],
	prof_id INTEGER -- example: ['7', '10'],
	salary TEXT -- example: ['med', 'high'],
	PRIMARY KEY (student_id, prof_id), 
	CONSTRAINT fk_ra_prof FOREIGN KEY(prof_id) REFERENCES prof (prof_id),
	CONSTRAINT fk_ra_student FOREIGN KEY(student_id) REFERENCES student (student_id)
)


CREATE TABLE course (
	course_id INTEGER -- example: ['2', '1'],
	name TEXT -- example: ['Machine Learning Theory', 'Intro to Database 1'],
	credit INTEGER -- example: ['2', '3'],
	diff INTEGER -- example: ['4', '3'],
	PRIMARY KEY (course_id)
)


CREATE TABLE prof (
	prof_id INTEGER -- example: ['2', '1'],
	gender TEXT -- example: ['Male', 'Female'],
	first_name TEXT -- example: ['Nathaniel', 'Zhihua'],
	last_name TEXT -- example: ['Pigford', 'Zhou'],
	email TEXT -- example: ['zzhihua@hku.hk', 'npigford0@hku.hk'],
	popularity INTEGER -- example: ['2', '3'],
	teachingability INTEGER -- example: ['5', '1'],
	graduate_from TEXT -- example: ['University of Washington', 'Beijing Polytechnic University'],
	PRIMARY KEY (prof_id)
)


CREATE TABLE registration (
	course_id INTEGER -- example: ['2', '1'],
	student_id INTEGER -- example: ['2', '3'],
	grade TEXT -- example: ['A', 'B'],
	sat INTEGER -- example: ['5', '4'],
	PRIMARY KEY (course_id, student_id), 
	CONSTRAINT fk_registration_course FOREIGN KEY(course_id) REFERENCES course (course_id),
	CONSTRAINT fk_registration_student FOREIGN KEY(student_id) REFERENCES student (student_id)
)


CREATE TABLE student (
	student_id INTEGER -- example: ['2', '1'],
	f_name TEXT -- example: ['Kerry', 'Chrysa'],
	l_name TEXT -- example: ['Dine-Hart', 'Pryor'],
	phone_number TEXT -- example: ['(243) 6836472', '(672) 9245255'],
	email TEXT -- example: ['kpryor0@hku.hk', 'cdinehart1@hku.hk'],
	intelligence INTEGER -- example: ['5', '2'],
	gpa REAL -- example: ['2.7', '2.4'],
	type TEXT -- example: ['RPG', 'TPG'],
	PRIMARY KEY (student_id)
)

Question: Give the grade score for Rik Unsworth in "Computer Network".
Evidence: 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;

SQL:
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' ) )