如何选择row_number和count over partition？

Question

我需要找到重复记录(具有主记录ID和重复记录ID):

select ciid, name from (
select ciid, name, row_number() over (
  partition by related_id, name order by updatedate desc) rn
) where rn = 1;

这为我提供了主记录ID,但它也包含没有重复的记录.

如果我使用

select ciid, name from (
select ciid, name, row_number() over (
  partition by related_id, name order by updatedate desc) rn
) where rn > 1;

这会获取所有重复记录,但不会记录主记录.

我希望我做的事情如下:

select ciid, name from (
select ciid, name, row_number()  over (
    partition by related_id, name order by updatedate desc
  ) rn, count(*)  over (
    partition by related_id, name order by updatedate desc
  ) cnt
) where rn = 1 and cnt > 1;

但我担心性能,甚至是它实际上做了我想要的.

如何仅为具有重复项的主记录获取主记录？请注意,这name不是唯一的列.只有ciid独一无二.

Answer 1

我最后在我的问题中使用了类似的查询:

select ciid, name from (
select ciid, name, row_number()  over (
    partition by related_id, name order by updatedate desc
  ) rn, count(*)  over (
    partition by related_id, name desc
  ) cnt
) where rn = 1 and cnt > 1;

工作得非常好.主记录是rn = 1,重复是rn> 1.确保count(*) over (partition ..)不能有order by子句.

Answer 2

我还没有测试过这个（因为我没有真实的数据，而且懒得创建一些），但似乎这些方面的东西可能会起作用：

with has_duplicates as (
  select related_id, name
  from yourtable
  group by related_id, name
  having count (*) > 1
),
with_dupes as (
  select
    y.ccid, y.name,
    row_number() over (partition by y.related_id, y.name order by y.updatedate desc) rn
  from
    yourtable y,
    has_duplicates d
  where
    y.related_id = d.related_id and
    y.name = d.name
)
select
  ccid, name
from with_dupes
where rn = 1