避免在SQL Server过程中进行访存

Question

I have a table with areas that looks like this:

ID     NAME          Coord
-------------------------
1     area1           bla
1     area2           bla
1     area3           bla

and a table with the position of an object depending on time:

Time_Stamp                    Latitude    Longitude
---------------------------------------------------
2018-07-17 21:13:30.000       bla         bla
2018-07-17 21:13:45.000       bla         bla
2018-07-17 21:14:00.000       bla         bla
2018-07-17 21:14:15.000       bla         bla
2018-07-17 21:14:30.000       bla         bla
2018-07-17 21:14:45.000       bla         bla
2018-07-17 21:15:00.000       bla         bla
2018-07-17 21:15:15.000       bla         bla
2018-07-17 21:15:30.000       bla         bla
2018-07-17 21:15:45.000       bla         bla
2018-07-17 21:16:00.000       bla         bla

From this I'm selecting a result set with the position of the object foreach area (type=> 0 outside area, 1 inside area)

TS                            area         type
-----------------------------------------------
2018-07-17 21:13:30.000       area1         1
2018-07-17 21:13:30.000       area2         0
2018-07-17 21:13:30.000       area3         0
2018-07-17 21:13:45.000       area1         0
2018-07-17 21:13:45.000       area2         0
2018-07-17 21:13:45.000       area3         0
2018-07-17 21:14:00.000       area1         0
2018-07-17 21:14:00.000       area2         1
2018-07-17 21:14:00.000       area3         0

From this dataset, I need to get the time foreach area when the object enters and gets out an area.something like:

TS                            area         type
------------------------------------------
2018-07-17 21:13:30.000       area1         1
2018-07-17 21:13:45.000       area1         0
2018-07-17 21:14:00.000       area2         1

and so long... I have a select in a fetch (foreach area).

select * 
from
    (select 
         min(ts) TS,
         area,
         type 
     from
         (select 
              *,
              grp = ROW_NUMBER() OVER(ORDER BY ts) -
                      ROW_NUMBER() OVER(PARTITION BY type ORDER BY ts)
          from 
              @t 
          where 
              area = @area    -- this is area from fetch and 
                              -- @t is the table I've built first
         ) a 
     group by 
         grp, type, area) b 
order by 
    endtime

I need a solution to avoid the fetch if this is posible.

Answer 1

I think you just need partition by :

      select min(ts) as TS, area, type 
      from (select t.*,
                   (row_number() over (partition by area order by  ts) -
                    row_number() over (partition by area, type order by ts)
                   ) as grp
            from @t t
           ) t 
      group by grp, type, area
      order by min(ts) desc;

The outer query is not necessary -- and endtime is not defined in your subquery anyway.