SQL递归CTE替代方案

Question

我有一项任务是在Redshift中合并重叠的时间范围。

这是一个很好的解决方案：Merge overlapping time intervals, how?

不幸的是，Redshift不支持递归CTE。如何转换此代码以执行它而不递归？

WITH RECURSIVE cte( id, date_start, date_end ) AS
(
  SELECT id, date_start, date_end
  FROM evento
  UNION 
  SELECT e.id,
         least( c.date_start, e.date_start ),
         greatest( c.date_end, e.date_end )
  FROM cte c
  JOIN evento e
  ON e.date_start between c.date_start and c.date_end
     OR 
     e.date_end between c.date_start and c.date_end
)
SELECT distinct date_start, date_end
FROM (
  SELECT id, 
         min( date_start) date_start, 
         max( date_end ) date_end
  FROM cte
  GROUP BY id
) xx
ORDER BY date_start;

http://www.sqlfiddle.com/#!12/bdf7e/9

Answer 1

您可以将日期与之前的行日期进行比较，并使用累积总和构建细分ID，如下所示：

WITH
prev_dates as (
    select id, date_start, date_end,
    lag(date_end) over (order by date_start) as prev_date_end
    from evento
),
sequences as (
    select *,
    sum(case when date_start>prev_date_end then 1 else 0 end) over (order by date_start) as sequence_id
    from prev_dates   
)
select 
sequence_id,
min(date_start) as date_stat,
max(date_end) as date_end
from sequences
group by 1