关于查询命令SELECT * FROM student WHERE sno IN(SELECT sno FROM sc WHERE cno = '1')，说法正确的是
A: 这是个连接查询
B: 这是个嵌套查询
C: 这个命令可以写成连接的形式
D: 这是个嵌套查询，它的子查询是不相关子查询
A: 这是个连接查询
B: 这是个嵌套查询
C: 这个命令可以写成连接的形式
D: 这是个嵌套查询，它的子查询是不相关子查询
举一反三
- 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
- 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));
- 查询选修1号课程的学生姓名的sql语句为： select sname from student where sno = (select sno from sc where cno=1);
- 查询选修了数学课(课程号为2)的学生人数,可以使用的查询语句是: 。 A: SELECT MAX(*) FROM SC WHERE Cno = 2; B: SELECT AVG(Sno) FROM SC WHERE Cno = 2; C: SELECT COUNT(*) FROM SC WHERE Cno = 2; D: SELECT COUNT(Sname) FROM SC WHERE Cno = 2;
- 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' );