มีนักแสดงกี่คน?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
How many actors are there?It is not neccessary to use all the tables.
 actor:  actor_id [ number]  name [ text]  musical_id [ number]  character [ text]  duration [ text]  age [ number] 
SELECT COUNT(*) FROM actor