• 2022-05-31
    基于“学生-选课-课程”数据库中如下三个关系:
    A: s↑.link:=p↑.link;p↑.link:=s
    B: q↑.link:=s;s↑.link:=p
    C: p↑.link:=s↑.link;s↑.link:=p
    D: p↑.link:=s;s↑.link:=q