急！请大侠们指点，一道数据库的题。写出关系代数表达式~~非常感谢！

Question

学生关系student(sno,sname,sex,birth,height,class,address)
课程关系course(con,cname,credit)
选修关系elective(sno,cno,grade)
用关系代数表达式表达下列查询：
1、检索学习课程号为C06的学生学号与成绩。
2、检索学习课程号为C06的学生学号和姓名。
3、检索学习课程名为ENGLISH的学生学号和姓名。
4、检索选修课程号为C02或C06的学生学号。
5、检索至少选修课程号为C02和C06的学生学号。
6、检索没有选修C06课程的学生姓名及其所在班级。
7、检索学习全部课程的学生姓名。
8、检索学习课程中包含了S08学生所学课程的学生学号。
非常感谢大侠们的关注，不过要求是用关系代数表达式表示哦，不是SQL语言哈~

Answer 1

1.use database_name
select s.sno,c.credit from course c join elective e
on c.con=e.con join student s
on s.sno=e.sno
where c.con='c06'

2..use database_name
select s.sname,c.sname from course c join elective e
on c.con=e.con join student s
on s.sno=e.sno
where c.con='c06'

3.select s.sname,c.sname from course c join elective e
on c.con=e.con join student s
on s.sno=e.sno
where c.cname='ENGLISH'

4..select s.sno from course c join elective e
on c.con=e.con join student s
on s.sno=e.sno
where c.cno in('c02','c06')

5...select s.sno from course c left join elective e
on c.con=e.con join student s
on s.sno=e.sno
where c.cno in('c02','c06')

6...select s.sno from course c left join elective e
on c.con=e.con join student s
on s.sno=e.sno
where c.cno not in('c02','c06')

7.select sname from student

8.select s.sno from course c left join elective e
on c.con=e.con join student s
on s.sno=e.sno
where s.sno like['s08'%]
呵呵，就这些了

Answer 2

关系代数的符号不好表达呀
两者理解起来都一样的……
很简单的

Answer 3

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