What classes did each school offer?
SELECT * ,  T3.school_code FROM CLASS AS T1 JOIN course AS T2 ON T1.crs_code   =   T2.crs_code JOIN department AS T3 ON T2.dept_code   =   T3.dept_code GROUP BY T3.school_code
classes offered by each school involves joining CLASS, course, and department tables; grouping by school_code indicates aggregation by each school;