建立数据库School其中存放以下三个表：学生Student学号姓名性别年龄系别即Sno char 3 Sname char4 Ssex char 2 Sage int Sdept char6；课程Course课程号课程名任课教师即Cno char3 Cname char8 teacher char4；选修SC学号课程号分数即Sno char 3 Cno char 3 Grade int。 查询男

1. 查询男生的选课记录

SELECT Student.Sno, Student.Sname, Course.Cname, SC.Grade FROM Student, Course, SC WHERE Student.Sno = SC.Sno AND Course.Cno = SC.Cno AND Student.Ssex = '男';

2. 查询选修了操作系统的学生姓名及系名

SELECT Student.Sname, Student.Sdept FROM Student, Course, SC WHERE Student.Sno = SC.Sno AND Course.Cno = SC.Cno AND Course.Cname = '操作系统';

3. 查询张三同学选修的所有课程的名称及其成绩

SELECT Course.Cname, SC.Grade FROM Student, Course, SC WHERE Student.Sno = SC.Sno AND Course.Cno = SC.Cno AND Student.Sname = '张三';

4. 查询计算机和数学专业学生所选修的课程详细信息，即课程号，课程名和任课教师

SELECT Course.Cno, Course.Cname, Course.teacher FROM Student, Course, SC WHERE Student.Sno = SC.Sno AND Course.Cno = SC.Cno AND (Student.Sdept = '计算机' OR Student.Sdept = '数学');

5. 查询女生所选修课程的平均成绩

SELECT Course.Cname, AVG(SC.Grade) FROM Student, Course, SC WHERE Student.Sno = SC.Sno AND Course.Cno = SC.Cno AND Student.Ssex = '女' GROUP BY Course.Cname