The takes table records which student took which course, in which semester and year. Its primary key has four columns: look for the key icons in its tab.

Compare the number of rows that SELECT DISTINCT returns with the number of rows of the table. The count shows next to each table name and above each result.

1. Return the different dept_name values of instructor.
2. Is {dept_name} a superkey of instructor? Answer yes or no.
3. Return the different combinations of id, semester and year in takes, in that column order.
4. Is {id, semester, year} a superkey of takes?
5. Return the different combinations of id and course_id in takes. Do two rows of today's data have the same pair?
6. A student who fails a course takes it again the next year. Is {id, course_id} a superkey of takes?