Identifying duplicate geometries in different layers with QGIS

Question

I'm using QGIS 3.16 Hannover under MacOS 10.13 environment. I've got two polygon shapefile layers: 'LIC' and 'ZEPA'. Some polygons (name, code & geometry) are present in both layers and I want to identify them by adding a new field to the layer 'ZEPA' with the value "yes" if that feature is also present in the other layer. I've tried in the field calculator the function overlay_equals(). My try has been

    array_to_string(overlay_equals('LIC', "yes"))

But it returns the new field empty (instead of "yes") for those equal features. What is wrong?

Answer 1

The following code actually does what I want:

CASE
    WHEN overlay_equals('LIC') = 1 THEN 'yes'
    ELSE NULL
END

Another option could be obtaining a 0/1 return, setting an integer field with the following expression:

overlay_equals('LIC')