Question

我需要根据列的所有值找到每行的两个最接近的距离。

我尝试进行交叉连接，并使用导数功能查找距离。我完全不确定怎么写。请提出建议。

select a.id,lead(a.value,b.value) as distance from cluster  a , cluster b

输入表：

ID  Values
1   12.1
2   11
3   14
4   10
5   9
6   15
7   16
8   8


ID  Values  Closest_Value
1   12.1    11,10
2   11       9,10
3   14      15,16
4   10       9,11
5   9        8,10
6   15      14,16
7   16      14,15
8   8        9,10

Answer 1

一种方法使用交叉连接和聚合：

select id, value,
       listagg(other_value, ',') within group (order by diff) as near_values
from (select c.id, c.value, c2.value as other_value
             abs(c2.value = c.value) as diff,
             row_number() over (partition by c.id order by abs(c2.value = c.value)) as seqnum
      from cluster c join
           cluster c2
           on c.id <> c2.id
     ) c
where seqnum <= 2
group by id, value;

对于大量数据，上述方法并不是特别有效。一种替代方法是使用lead()和lag()来获取值，取消透视和聚合：

with vals as (
      select c.id, c.value,
             (case when n.n = 1 then prev_value_2
                   when n.n = 2 then prev_value
                   when n.n = 3 then next_value
                   when n.n = 4 then next_value_2
              end) as other_value
      from (select c.*,
                   lag(value, 2) over (order by value) as prev_value_2,
                   lag(value) over (order by value) as prev_value,
                   lead(value) over (order by value) as next_value,
                   lead(value, 2) over (order by value) as next_value_2,
            from clusters c
           ) c cross join
           (select rownum as n
            from clusters
            where rownum <= 4
           ) n  -- just a list of 4 numbers
       )
select v.id, v.value,
       list_agg(other_value, ',') within group (order by diff)
from (select v.*,
             abs(other_value - value) as diff
             row_number() over (partition by id order by abs(other_value - value)) as seqnum
      from vals v
     ) v
where seqnum <= 2
group by id, value;

列的最近距离

1 个答案: