สนามพรมมีกี่สนาม ?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
how many were carpet courts ?It is not neccessary to use all the tables.
 table_204_638:  id [ number]  "year" [ number]  "tournament" [ text]  "surface" [ text]  "round" [ text]  "winner" [ text]  "score" [ text] 
SELECT COUNT(*) FROM table_204_638 WHERE "surface" = 'carpet'