The professors table is almost ready now. However, it still allows for NULLs to be entered. Although some information might be missing about some professors, there's certainly columns that always need to be specified.

-- Disallow NULL values in firstname
ALTER TABLE professors 
ALTER COLUMN firstname SET NOT NULL;


-- Disallow NULL values in lastname
ALTER TABLE professors
ALTER COLUMN lastname
SET NOT NULL;


-- Make universities.university_shortname unique
ALTER TABLE universities
ADD CONSTRAINT university_shortname_unq UNIQUE(university_shortname);


-- Make organizations.organization unique
ALTER TABLE organizations
ADD CONSTRAINT organization_unq UNIQUE(organization)