根据多列删除重复项

Question

我使用以下内容列出了重复项:

select s.MessageId, t.* 
from Message s
join (
    select ToUserId, FromUserId, count(*) as qty
    from Message
    group by ToUserId, FromUserId
    having count(*) > 1
) t on s.ToUserId = t.ToUserId and s.FromUserId = t.FromUserId

现在,如何删除除一条消息之外的所有消息(我正在尝试删除重复项,以便我可以应用唯一索引FromUserId and ToUserId).

Answer 1

使用a cte并指定行号,以便删除除重复对之外的所有行号.

with rownums as 
(select m.*, 
 row_number() over(partition by ToUserId, FromUserId order by ToUserId, FromUserId) as rnum
 from Message m)
delete r
from rownums r
where rnum > 1