[Qgis-user] Using aggregates functions to count intersected features from another layer

[Nathan Woodrow]

Maybe using a virtual layer query via DB Manager will work.  You have full
SQL join support. Speed isn't always the best but gives you the full power
of SQL which is the correct way to do this IMO.

E.g SELECT LayerA.id, COUNT(*) FROM layerA
JOIN layerB ON ST_WithIn(layerA.geometry, layerB.geometry)
GROUP BY layerA.type

Although you can't do an update but you can make a new layer with the new
counts.

- Nathan

On Wed, Oct 19, 2016 at 10:22 PM, Neumann, Andreas <a.neumann at carto.net>
wrote:

> Well yes - but that is not a "live" point in polygon. It create separate
> layers which need to be kept up-to-date.
>
> Harrissou was after a "live" point in polygon, which is automatically kept
> up-to-date through a QGIS expression.
>
> Maybe Nyall knows how to write the correct aggregate expression for that?
>
> Greetings,
>
> Andreas
>
> On 2016-10-19 14:11, Nicolas Cadieux wrote:
>
>
> Try this.
>
> http://www.qgistutorials.com/fr/docs/points_in_polygon.html
>
> Nicolas
>
> Le 19 oct. 2016 à 06:37, DelazJ [via OSGeo.org] <[hidden email]> a écrit :
>
> Hi,
>
> I have a polygon layer and a point one.
> I'd like to calculate for each polygon feature, the number of points that
> it covers. I thought the aggregates functions could help me find an easier
> and straight expression to perform this (without creating intermediate
> layers) but I fail to find any correct syntax.
>
> I tried aggregate ('mypoint', 'count', "id", intersects ($geometry,
> geometry($currentfeature)))
>
>  And many variants of the fourth option but It always return the total of
> points or an error. Actually this option is a filter and I wonder if i'm
> not missing a "group by" option in the aggregate function (which seems to
> be the appropriate one in my case). Is it possible?
> The work around I found is to populate an ad'hoc field in the point layer
> with overlapping polygon id, thanks to the SpatialJoin plugin, then I
> create a one-to-many relation in the project between the two layers in
> other to use relation_aggregate function.
> But I expected something more direct.
>
> Any hint, please?
>
> Thanks,
> Harrissou
>
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