select a.classid 班级ID,a.classname 班级名称,nvl(b.studentno,0) 学生数 from class a, ( select classid,count(0) studentno from student group by classid ) b where a.classid=b.classid(+);
试试这个 select a.classid,a.classname,count(b.classid) from class a,student b where a.classid = b.classid group by a.classid,a.classname
select a.classid, a.classname, count(b.studentid) from class a,student b where a.classid = b.classid group by a.classid,a.classname
(
select classid,count(0) studentno from student group by classid
) b
where a.classid=b.classid(+);
select a.classid,a.classname,count(b.classid)
from class a,student b
where a.classid = b.classid
group by a.classid,a.classname
where a.classid = b.classid group by a.classid,a.classname