已知学生选课信息表：sc（sno，cno，grade）。查询“至少选修了一门课程，但没有学习成绩的学生学号和课程号”的SQL语句是（ ）。 A: SELECT sno,cno FROM sc WHERE grade=NULL B: SELECT sno,cno FROM sc WHERE grade IS C: SELECT sno,cno FROM sc WHERE grade IS NULL D: SELECT sno,cno FROM sc WHERE grade=

‏检索选修课程“C2”的学生中成绩最高的学生的学号。正确的SELECT语句是（）。‍ A: SELECT SNO FROM SC WHERE CNO='C2' AND GRADE >= ( SELECT GRADE FORM SC WHERE CNO='C2' ); B: SELECT SNO FROM SC WHERE CNO='C2' AND GRADE IN ( SELECT GRADE FORM SC WHERE CNO='C2' ); C: SELECT SNO FROM SC WHERE CNO='C2' AND GRADE NOT IN ( SELECT GRADE FORM SC WHERE CNO='C2' ); D: SELECT SNO FROM SC WHERE CNO='C2' AND GRADE >= ALL ( SELECT GRADE FORM SC WHERE CNO='C2' );

查询编号为'c01'的课程考试成绩在80-89之间的学生的学号,下列（）语句不能实现。 A: select sno ,grade from sc where cno='c01' and grade between 80 and 89 B: select sno ,grade from sc where cno='c01' and grade>=80 and grade<90 C: select sno ,grade from sc where cno='c01' and not (grade90) D: select sno ,grade from sc where cno='c01' and grade in (80-89)

查询最低成绩大于85分的学生学号和平均成绩,可以使用的查询语句是:　 。 A: SELECT Sno, AVG(Grade) FROM SC HAVING MIN(Grade) > 85 GROUP BY Sno; B: SELECT Sno, AVG(Grade) FROM SC GROUP BY Sno HAVING MIN(Grade) > 85; C: SELECT Sno, AVG(Grade) FROM SC WHERE MIN(Grade) > 85 GROUP BY Sno; D: SELECT Sno, AVG(Grade) FROM SC GROUP BY Sno WHERE MIN(Grade) > 85;

已知关系模式：sc(sno,sname,grade)，各属性含义依次为学号、课程名、分数。要查找“数据库”课分数最高的学生的学号，正确的SQL语句是 A: SELECT sno FROM sc WHERE sname = "数据库" AND grade = MAX(grade) B: SELECT sno FROM sc FOR sname = "数据库" OR grade＞=MAX(grade) C: SELECT sno FROM sc WHERE sname = "数据库" AND grade = (SELECT MAX(grade) FROM sc) D: SELECT sno FROM sc FOR sname = "数据库" OR grade = (SELECT MAX(grade) FROM sc)