query: SELECT classroom ,  count(DISTINCT grade) FROM list GROUP BY classroom
question: For each classroom, show the classroom number and count the number of distinct grades where uses the room.
query_toks: SELECT classroom , count ( DISTINCT grade ) FROM list GROUP BY classroom
query_toks_no_value: select classroom , count ( distinct grade ) from list group by classroom
question_toks: For each classroom, show the classroom number and count the number of distinct grades where uses the room.