针对S_T数据库，查询既选修了1号课程又选修3号课程的学生学号，以下不正确的SQL命令是（ ）。 A: select snofrom scwhere cno='1' and cno='3' B: select snofrom scwhere cno='1'intersectselect snofrom scwhere cno='3' C: select snofrom scwhere cno='1' and sno in(select snofrom scwhere cno='3') D: select a.snofrom sc a,sc bwhere a.sno=b.sno and a.cno='1' and b.cno='3'

A．SELECT Cno, AVG(Score) FROM SCS GROUP BY Score ORDER BY 2, Cno Desc B．SELECT Cno, AVG(Score) FROM SCS GROUP BY Cno ORDER BY 2, Cno Desc C．SELECT Cno, AVG(Score) FROM SCS WHERE Cno, Desc GROUP BY Score D．SELECT Cno, AVG(Score) FROM SCS GROUP BY, AVG(Score) ORDER BY, Cno Desc

检索选课人数少于4人的课程号。正确的SQL语句是( ) A: SELECT CNO FROM SC WHERE COUNT(*)<;4 B: SELECT CNO FROM SC GROUP BY CNO HAVING COUNT(*)<;4 C: SELECT DISTINCT CNO FROM SC ORDER BY CNO D: SELECT CNO FROM SC WHERE COUNT(CNO)<;4

在“学生-选课-课程”数据库中的3个关系如下：S（SNO, SNAME, SEX, AGE）； C（CNO, CNAME, TEACHER）；SC（SNO, CNO, GRADE），查询既选修了“2”号又选修了“4”号课程的学生学号。若用关系代数表达式来表示为（ ）。 A: ПSNO (σCNO=’2’(SC) ∩ σCNO=’4’(SC) ) B: ПSNO (σCNO=’2’(SC)) ¥ ПSNO(σCNO=’4’(SC) ) C: ПSNO (σCNO=’2’(SC) ∪ σCNO=’4’(SC) ) D: σCNO=’2’(SC) ¥σCNO=’4’(SC)

在MySQL中,假设有学生选课表SC(sno,cno,score)。那么列出所有选修课程超过5门的学生学号以及选修课程数目,其正确的SQL语句为()。 A: select sno,count(cno)from scwhere count(cno)>=5; B: select sno,count(cno)from scgroup by sno where count(cno)>=5; C: select sno,count(cno)from scgroup by sno having count(cno)>=5; D: select sno,count(cno)from scgroup by cno having count(cno)>=5;

统计每门课程的选课人数select cno , _________from scgroup by ________ A: count(*) ; cno B: count(sno) ; cno C: count(*) ; sno D: count(sno) ; sno

‏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' );

检索选修了课程”C1”的学生中成绩最高的学生的学号，正确的SELECT语句为（ ） A: SELECT Sno FROM SC WHERE Cno=’C1’ AND GRADE &gt;=ALL (SELECT Grade FROM SC WHERE Cno=’C1’); B: SELECT Sno FROM SC WHERE Cno=’C1’ AND GRADE IN (SELECT Grade FROM SC WHERE Cno=’C1’); C: SELECT Sno FROM SC WHERE Cno=’C1’ AND GRADE &gt; ANY (SELECT Grade FROM SC WHERE Cno=’C1’); D: SELECT Sno FROM SC WHERE Cno=’C1’ AND GRADE &gt;= (SELECT Grade FROM SC WHERE Cno=’C1’);

基于学生—选课—课程数据库中的三个基本表：学生的信息表：STUDENT(sno, sname, sex, age, dept)主码为sno课程信息表：COURSE(cno,cname, teacher)主码为cno学生选课信息表：SC(sno, cno, grade)主码为(sno, cno) “查询没有学习成绩的学生的学号和课程号”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="

查询实现同时选修了C1和C2号课程的学生学号，下列代码正确的是（ ）。 A: SELECT sno FROM SC WHERE Cno='C1' AND Cno='C2'; B: SELECT sno FROM SC WHERE Cno='C1' AND Sno IN ( SELECT sno FROM SC WHERE Cno='C2' );