问大家一个SQL语句~~
create   table   student
(
    sid   char(10)   primary   key,
    sname   varchar(10),
    birth   date,
    status   char(6),
    sex   char(4),
    check(status   in   ( 'in ', 'out ')),
    check(sex   in   ( 'M ', 'F '))
);

create   table   course
(
    cid   char(2)   primary   key,
    cname   varchar(20),
    time   number(3),
    leader   char(10),
    choose   char(6),
    foreign   key   (leader)   references   student   (sid),
    check   (time   in   ( '40 ', '80 ', '120 ', '160 ')),
    check   (choose   in   ( 'must ', 'may '))  
);

create   table   exam
(
    eid   varchar(5)   primary   key,
    cid   char(2),
    edate   date,
    num   char(10),
    foreign   key   (cid)   references   course(cid),
    check   (num   in   ( '1st ', '2nd '))         //num为第几次考,1st代表1次,2nd代表补考
);

create   table   score
(
    sid   char(10),
    eid   varchar(5),
    grade   number(4,1),
    pass   char(10),
    primary   key   (sid,eid),
    foreign   key   (sid)   references   student   (sid),
    foreign   key   (eid)   references   exam   (eid),
    check   (pass   in   ( 'yes ', 'no ', '2nd '))   //pass看是通过,不通过,补考通过
);


使用UPDATE语句修改课代表
针对每门课程，将课代表改为本课程成绩最高、且非补考的人


------解决方案--------------------
还是LZ写的不清楚,多写几个注释,都不太清楚你要更新的字段,大概的更新方法,只是找出名字来更新到leader字段了,没测试.
update course set leader =(
select sname from student t1,(
select sid from score where grade =(select max(grade) from score where pass = 'yes ') where pass = 'yes ' and rownum=1) t2
where t1.sid=t2.sid)
还有就是如果有两个人同样是最高成绩怎么办??