CREATE TABLE list (lastname CLOB, firstname CLOB, grade NUMBER, classroom NUMBER)
CREATE TABLE teachers (lastname CLOB, firstname CLOB, classroom NUMBER)

For each grade, return the grade number, the number of classrooms used for the grade, and the total number of students enrolled in the grade.
SELECT grade, COUNT(DISTINCT classroom), COUNT(*) FROM list GROUP BY grade
SELECT "grade", COUNT(DISTINCT "classroom"), COUNT(*) FROM "list" GROUP BY "grade"