Give the grade score for Rik Unsworth in "Computer Network".
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' ) )