4.19

Under what circumstances would the query

SELECT * 
FROM student NATURAL FULL OUTER JOIN takes 
   NATURAL FULL OUTER JOIN course

include tuples with null values for the title attribute?

  1. If the course already had a null value for the title attribute. This is a valid circumstance since there is no NOT NULL domain constraint in the schema of course relation.

  2. If a student takes a course that is not given by his/her department. (Recall that dept_name attribute appears in both course relation and student relation).