Students Who Completed All Required Courses

Return the students who have completed every course listed in Required. Order by student.

Table schema

Required(course VARCHAR(20) PRIMARY KEY)
Completed(student VARCHAR(20), course VARCHAR(20))

Sample data

Required: Math, Physics

Completed:
student | course
Amy | Math
Amy | Physics
Ben | Math
Cara | Math
Cara | Physics
Cara | Chem