要去掉结果表中的重复行,可用DING SELECT DISTINCT SnO from so Cno Grade冰kb 195121011c0190必修 29512101c0286选修 sho 39512101c06NULL必修 19512101 49512102c0278选修 29512102 59512102c0466必修 39521102 69521102c0182选修 9521102c0275选修 49521103 89521102c0492必修 59531101 99521102c0550必修 69531102 109521103c0268选修 119521103c06NUL必修 29531101c0180选修 139531101 95必修 149531102 5 85必修要去掉结果表中的重复行,可用DISTINCT SELECT DISTINCT Sno FROM SC