Sql 如何从同一个表中选择唯一元组

我想找到所有在两个或两个以上部分注册的不同学生对

注册SID*，等级，dname*，cno*，部门号*

---

如果每个节由dname*、cno*、sectno*唯一标识，则可以在标识节的列上进行自联接，并指定e1.sid

select e1.sid, e2.sid from enroll e1
join enroll e2 on e1.dname = e2.dname
and e1.cno = e2.cno
and e1.secno = e2.sectno
where e1.sid < e2.sid
group by e1.sid, e2.sid
having count(*) > 1

但是，如果一个sid在同一节上注册多次，则此查询将无法正常工作

with enroll as (
select 1 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 1 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 2 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 3 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 3 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 1 sid, 'dname' dname, 2 cno, 2 secno from dual union all
select 2 sid, 'dname' dname, 2 cno, 2 secno from dual
)
select rn,sid from (
select row_number() over (partition by sid order by dname) as rn ,sid
from enroll ) 
where rn>1

使用行号

如果一个sid在同一节上注册多次，则此查询将正常工作

with enroll as (
select 1 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 1 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 2 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 3 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 3 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 1 sid, 'dname' dname, 2 cno, 2 secno from dual union all
select 2 sid, 'dname' dname, 2 cno, 2 secno from dual
)
select rn,sid from (
select row_number() over (partition by sid order by dname) as rn ,sid
from enroll ) 
where rn>1

如果需要，可以使用distinct

with enroll as (
select 1 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 1 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 2 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 3 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 3 sid, 'dname' dname, 1 cno, 1 secno from dual union all
select 1 sid, 'dname' dname, 2 cno, 2 secno from dual union all
select 4 sid, 'dname' dname, 2 cno, 2 secno from dual union all
select 2 sid, 'dname' dname, 2 cno, 2 secno from dual
)
select distinct  sid from (
select row_number() over (partition by sid order by dname) as rn ,sid
from enroll ) 
where rn>1

输出

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但我想让这对学生一起参加2个或更多的课程。上面的查询给出了在一个节中注册的一对together@anvitapotluri请参阅更新，而不是使用组和

>        SID
> ----------
>          1
>          2
>          3