3、 Switch2为根交换机;因为Switch2的优先级为0,优先级最高; Switch1 E0/0;Switch3 E0/1;Switch3 E 0/0;这些端口到达根网桥的开销最小,并且端口ID最小,优先级最高。
答案:
1、 alter table S add (sdep char(30))
2、 select s.sname,sc.score from s,c,sc where s.sno=sc.sno
and c.cno=sc.cno and c.cname=’ 计算机网络’ order by sc.score desc
或者 select s.sname,sc.score from s,sc where s.sno=sc.sno and sc.cno in (select cno from c where c.cname=’ 计算机网络’) order by sc.score desc
或者select s.sname,sc.score from s,sc where s.sno=sc.sno and exists (select 1 from c where c.cname=’ 计算机网络’ and sc.cno=c.cno) order by sc.score desc
3、
insert into c (cno,cname) values(12,’数据库’)