ค้นหาจำนวนห้องที่อยู่ในแต่ละชั้น ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
Find the number of rooms located on each block floor.It is not neccessary to use all the tables.
 room:  roomnumber [ number]  roomtype [ text]  blockfloor [ number]  blockcode [ number]  unavailable [ boolean] 
SELECT COUNT(*), T1.blockfloor FROM block AS T1 JOIN room AS T2 ON T1.blockfloor = T2.blockfloor AND T1.blockcode = T2.blockcode GROUP BY T1.blockfloor