现要查找缺少成绩(Grade)的学生学号(Snum),相应的SQL语句是
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现要查找缺少成绩(Grade)的学生学号(Snum),相应的SQL语句是
A.SELECTSnumFROMSCWHEREGrade=0
B.SELECTSnumFROMSCWHEREGrade<=0
C.SELECTSnumFROMSCWHEREGrade=NULL
D.SELECTSnumFROMSCWHEREGradeISNULL
参考答案: