qgis - Select polygons with other polygons layer?

I have to select some polygons with another polygon layer. I have to select green polygons using relevant overlapping percentage with the purple ones. In this particular example, I would like to select all green polygons except the third one from starting from above for example.

Do you have any advice to do that?

Answer

I am not sure how best we can define "adequate". But assuming over 50% of the green polygon is overlapping with purple:

1. Go to Layer | Add Layer | Add/Edit Virtual Layer


2. [Import] (greens and purples) layers

An example of query is:

SELECT greens.*   FROM greens, purples

WHERE st_area(st_intersection(greens.geometry, purples.geometry)) 
      > 0.5 * st_area(greens.geometry) 

If you need a higher threshold e.g. 'at least 60% of green polygon has to overlap with purple' then change 0.5 to 0.6.

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If you want to decide it by the greens' centroids' location.

SELECT greens.*   FROM greens, purples
WHERE st_within(st_centroid(greens.geometry), purples.geometry) = 1