[postgis-users] Count Points in Polygon with Postgis

[Tom van Tilburg]

Hi Carsten,

What you need is a *left join* :

|select grid.gid, count(kioskdhd3.geom) AS totale
FROM grid
LEFT JOIN kioskdhd3
ON st_contains(grid.geom,kioskdhd3.geom)
GROUP BY grid.gid;|

Note that I changed the * in count to a column from your points table 
because you only want to count when you have a non-null value in your 
points table.

Regards,
  Tom

On 16-3-2013 16:53, Carsten Hogertz wrote:
>
> I've got a simple problem: I want to count the number of points within 
> a set of polygons.
>
> I have a SQL already but it only gives back the gid of the polygone 
> that actually contains points.
>
> My tables: a polygon layer with 19.000 rows and a point layer with 450 
> rows.
>
> The following SQL
>
> |select grid.gid, count(*) AS totale FROM grid, kioskdhd3 WHERE
> st_contains(grid.geom,kioskdhd3.geom) GROUP BY grid.gid;
> |
>
> return only some 320 polygons that actually contain points. But I want 
> all polygons returned, even thought the number of points is 0.
>
> Of course it has to do with my WHERE-clause. Where do I have to put in 
> my st_contains?
>
> Thank you Carsten
>
>
>
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