Question

In sql server 2005, I have a parent table describing paths, and a child table which contains the coordinates for each point along each path, like this:

Path

int path_id, string path_name

Points

int path_id, float x, float y, int n

The first point on the path is n=1, and then each new point that is added increments n.

What I need to do is, delete the points returned by this:

select [path_id]
from Points
where n=1

i.e. the first point in each path, and then also delete all the points where n is the value returned by this:

select [path_id], max(n)
from Points
group by [path_id]

i.e. the last added point to each path.

For the first part, I can do this:

delete from Points
where n=1

but how do I do the second part?

Answer 1

DELETE FROM Points
FROM points
INNER JOIN     
(SELECT point_id, path_id, n
 FROM (SELECT ROW_NUMBER() OVER(PARTITION BY path_id ORDER BY n DESC) AS RowNumber, 
              point_id, path_id, n
       FROM points ) t
  WHERE n = 1 or RowNumber = 1 
) t on t.point_id = points.point_id and t.path_id = points.path_id and t.n = points.n