Which student failed the course Intro to Database 2? Please give his or her full name.
If grade is NULL, it means that this student fails to pass the course; full name refers to f_name and l_name;
SELECT T1.f_name, T1.l_name FROM student AS T1 INNER JOIN registration AS T2 ON T1.student_id = T2.student_id INNER JOIN course AS T3 ON T2.course_id = T3.course_id WHERE T2.grade IS NULL AND T3.name = 'Intro to Database 2'