如何获得每个岛屿的第一排和最后一排？

Question

所以我最近在一个问题上得到了很好的帮助。但是，我需要更精确一些，希望可以在SQL中实现。

这是我的最后一个问题：

• Select only rows that has a column changed from the rows before it, given an unique ID

我的细微差别是：

personID | status | unixtime | column d | column e | column f
    1        2       213214      x            y        z
    1        2       213325      x            y        z
    1        2       213326      x            y        z
    1        2       213327      x            y        z
    1        2       213328      x            y        z <-- I want this
    1        3       214330      x            y        z <-- Any of this is OK     
    1        3       214331      x            y        z
    1        3       214332      x            y        z <-- I want this or
    1        2       324543      x            y        z <-- I want this

因此，我要不是岛的起点，而是要岛的终点。如果我介于两者之间，那完全可以，最好是到此为止。但是我真的希望状态改变的“在...之前”和“在...之后”是什么，如果有任何意义的话。这可能是特定状态。

Answer 1

select t.*
from (select t.*, 
       case when status <> lag(status,1,NULL) over(partition by personID order by unixtime) 
            then 1
            when lag(status,1,NULL) over(partition by personID order by unixtime) is null
            then 1
            else 0 end as start_status,
       case when status <> lead(status,1,NULL) over(partition by personID order by unixtime) 
            then 1
            when lead(status,1,NULL) over(partition by personID order by unixtime) is null
            then 1
            else 0 end as end_status
      from mytable t
) t
where end_status = 1
--or start_status = 1    -- uncomment this line if you want start statuses as well

Answer 2

此查询将产生所有终止或启动分区的行（或在单行分区的情况下都行）：

SELECT *
FROM  (
   SELECT *
        , lag(status)  OVER w IS DISTINCT FROM status AS partition_start
        , lead(status) OVER w IS DISTINCT FROM status AS partition_end
   FROM   tbl
   WINDOW w AS (PARTITION BY personID ORDER BY unixtime)
   ) sub
WHERE (partition_start OR partition_end)
ORDER  BY personID, unixtime;

db <>小提琴here