逐列获取最后一个非空值，其中列按日期排序

Question

select *
from example;

edate   userid  status
2022-05-01  abc123  true
2022-05-02  abc123  (null)
2022-05-03  abc123  (null)
2022-05-04  abc123  (null)
2022-05-05  abc123  false
2022-05-06  abc123  (null)
2022-05-07  abc123  (null)
2022-05-08  abc123  (null)
2022-05-09  abc123  true
2022-05-10  abc123  (null)

我想写一个新字段，'status_backfilled' 基于 userId 的最新数据点。

在示例数据中，用户状态在 5 月 1 日为 true，然后直到 5 月 5 日为 null。因此，我希望新字段在 5 月 1 日至 5 月 4 日之间为真。然后状态切换为 false。这个值直到 5 月 9 日都没有变化，所以我想要在 5 月 5 日到 8 日之间为 false，然后再次为 true。

期望的输出：

select *
from example_desired;

edate   userid  status_backfilled
2022-05-01  abc123  true
2022-05-02  abc123  true
2022-05-03  abc123  true
2022-05-04  abc123  true
2022-05-05  abc123  false
2022-05-06  abc123  false
2022-05-07  abc123  false
2022-05-08  abc123  false
2022-05-09  abc123  true
2022-05-10  abc123  true

如何按列合并以获得数据已排序的用户的最新非空状态，在本例中是按日期？

Answer 1

您可以通过使用一些 window 函数来实现您想要的结果 -

WITH grp AS (SELECT edate, userid, status,
                    CASE WHEN status IS NULL THEN 0
                         ELSE ROW_NUMBER() OVER(ORDER BY edate)
                     END RN
               FROM example
           ),
grp_sum AS (SELECT edate, userid, status, SUM(RN) OVER(ORDER BY edate) grp_sum
              FROM grp
           )
SELECT edate, userid,
       FIRST_VALUE(status) OVER(PARTITION BY grp_sum ORDER BY status NULLS LAST) status_backfilled 
  FROM grp_sum;

Demo.

Answer 2

实际上，甚至更好:

select e1.edate, e1.userId, coalesce(e1.status, t.status) as status
from example e1
cross join lateral ( 
   select status from example e2 
   where e1.userid = e2.userid 
   and e1.edate > e2.edate 
   and e2.status is not null 
   order by e2.edate desc limit 1 
 ) t

fiddle

这是另一种方式：

with cte as (
  select e.* ,e_s.edate s_edate, e_s.status s_status , row_number() over (partition by e.userid,e.edate order by e_s.edate desc) rn  
  from example e
  left join (
    select * 
    from example
    where status is not null 
  ) e_s on e.userid = e_s.userid 
        and e_s.edate < e.edate 
) 

select edate, userId, coalesce(status, s_status) as status
from cte where rn = 1

逐列获取最后一个非空值，其中列按日期排序

Get last non null value columnwise where column is sorted by date

sql

postgresql