Tom Glavine ผู้เล่นมีกี่ตำแหน่ง?ไม่จำเป็นต้องใช้ตารางทั้งหมด
How many positions is player Tom Glavine?It is not neccessary to use all the tables.
 table_21721351_18:  (position [ VARCHAR ] player [ VARCHAR) ]
SELECT COUNT(position) FROM table_21721351_18 WHERE player = "Tom Glavine"