数据库编程实现学生均分评价

declare 
  line student%rowtype;
  amk mark.cmark%type;
begin
  for line in (select * from student) loop
    select avg(cmark) into amk from mark where sid=line.sid group by sid;
    if amk>80 then
      dbms_output.put_line(line.sname||'均分为'||amk||'，成绩优秀');
    elsif amk>70 then 
      dbms_output.put_line(line.sname||'均分为'||amk||'，成绩良好');
    else
      dbms_output.put_line(line.sname||'均分为'||amk||'，成绩较差');
    end if;
    end loop;
    end;