How many students play Works of Widenius?
SELECT count ( distinct t1.StuID )  FROM Plays_games AS T1 JOIN Video_games AS T2 ON T1.gameid   =   T2.gameid where t2.GName  =  "Works of Widenius"
counting students = count(distinct StuID); play = JOIN on Plays_games and Video_games on gameid; Works of Widenius refers to GName in Video_games;