มีกี่ประเทศที่ได้รับเหรียญเงิน ?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
how many nations received silver medals ?It is not neccessary to use all the tables.
 table_203_739:  id [ number]  "rank" [ number]  "nation" [ text]  "gold" [ number]  "silver" [ number]  "bronze" [ number]  "total" [ number] 
SELECT COUNT("nation") FROM table_203_739 WHERE "silver" <> 0