ค้นหาจำนวนห้องที่อยู่ในแต่ละชั้น ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
Find the number of rooms located on each block floor.It is not neccessary to use all the tables.
 room:  (blockfloor [ VARCHAR ] blockcode [ VARCHAR) ]
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