SQL语句:select student.* , cno, grade from student, sc where student.sno=sc.sno 实现了关系代数中的()操作。
A: 笛卡尔积
B: 等值连接
C: 自然连接
D: 除
A: 笛卡尔积
B: 等值连接
C: 自然连接
D: 除
举一反三
- 【多选题】针对学生选课数据库S_T,以下()操作实现了student表与sc之间的自然连接。 A. select student.* , cno, grade from student join sc on student.sno=sc.sno B. select student.* , sc.* from student , sc where student.sno=sc.sno C. select student.sno, sname, ssex, sage, sdept , cno, grade from student , sc where student.sno=sc.sno D. select student.* , cno, grade from student , sc where student.sno=sc.sno
- 在学生选课数据库中,查询选修了课程的学生的学号、姓名,SQL语句可为( ) A: SELECT DISTINCT Sno, Sname FROM Student, SC WHERE Student.Sno = SC.Sno; B: SELECT Sno, Sname FROM Student, SC WHERE Student.Sno = SC.Sno; C: SELECT DISTINCT Sno, DISTINCT Sname FROM Student WHERE Student.Sno IN (SELECT Sno FROM SC); D: SELECT Sno, Sname FROM Student WHERE Student.Sno IN (SELECT DISTINCT Sno FROM SC);
- 查询每个学生的学号、姓名、选修的课程名及成绩,下列()的操作是正确的。 A: select student,sno,sname,grade from student,sc where student.sno=sc.sno and sc.cno=course.cno B: select student,sno,sname,grade from student,sc,cource where student.sno=sc.sno C: select student,sno,sname,grade from student,sc,cource where sc.cno=course.cno D: select student,sno,sname,grade from student,sc,cource where student.sno=sc.sno and sc.cno=course.cno
- 下列查询中,属于相关子查询的有()。 A: SELECT * FROM student WHERE sno IN (SELECT sno FROM sc WHERE cno='1'); B: SELECT sno, cno FROM SC x WEHRE grade>=(SELECT AVG(grade) FROM SC y WHERE y.sno = x.sno); C: SELECT sname FROM student WHERE EXISTS(SELECT * FROM sc WHERE sno=student.sno AND cno='1'); D: SELECT sname FROM student WHERE NOT EXISTS(SELECT * FROM course WHERE NOT EXISTS(SELECT * FROM sc WHERE sc.sno=student.sno AND sc.cno=course.cno));
- 以下命令是相关子查询的嵌套查询是: A: SELECT * FROM student WHERE sno IN (SELECT sno FROM sc WHERE cno = '1') B: SELECT * FROM student WHERE EXISTS (SELECT * FROM sc WHERE cno = '1' AND sc.sno = student.sno) C: SELECT sno, cno FROM sc x WHERE grade>(SELECT AVG(grade) FROM sc y WHERE y.sno = x.sno) D: 以上都是