รอบเบื้องต้นแข่งกี่คน ?ไม่จำเป็นต้องใช้ทุกโต๊ะ
how many drivers raced in the preliminary round ?It is not neccessary to use all the tables.
 table_203_780:  id [ number]  "rank" [ number]  "diver" [ text]  "preliminary\npoints" [ number]  "preliminary\nrank" [ number]  "final\npoints" [ number]  "final\nrank" [ number]  "final\ntotal" [ number] 
SELECT COUNT("diver") FROM table_203_780 WHERE NOT "preliminary\npoints" IS NULL