Table schema:
CREATE TABLE department (school_code VARCHAR, dept_code VARCHAR); CREATE TABLE CLASS (crs_code VARCHAR); CREATE TABLE course (crs_code VARCHAR, dept_code VARCHAR)

Question: Find the number of classes in each school.
SQL: SELECT COUNT(*), 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