ทีม Norton มี 0 คะแนนและคลาส 350cc ในปีใด?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
In what Year did the Norton Team have 0 Points and 350cc Class?It is not neccessary to use all the tables.
 table_name_81:  (year [ INTEGER ] points [ VARCHAR ] class [ VARCHAR ] team [ VARCHAR) ]
SELECT AVG(year) FROM table_name_81 WHERE class = "350cc" AND team = "norton" AND points < 0