Query three tables with join
SELECT DISTINCT sectionname , 
               sectionid 
FROM   section 
       LEFT JOIN classsection 
              ON classsection.fk_section_sectionid = section.sectionid 
       LEFT JOIN classes 
              ON classid = classsection.fk_class_classid 
       LEFT JOIN course 
              ON courseid = fk_course_courseid 
WHERE  coursename = 'School'


i just joined section and classses first and then joined courses to see the department name which sections are belong to which classes and it worked kudos