Select duplicate geometries in a single layer in QGIS

Removing duplicate geometries and features is fairly straightforward in QGIS but what if you want to select and extract the features with duplicates or the features and their duplicates? In this video, we use a query in the DB Manager and the "Select by location" algorithm to do just that.
Read more: bnhr.xyz/2020/12/09/select-du...
CHAPTERS
00:00 - Introduction
00:39 - Checking for duplicate geometries using the Topology Checker plugin
01:45 - Using DB Manager to get geometries with duplicates
03:59 - Load the SQL result as new layer in QGIS
05:12 - Get all duplicate features using the Select by location algorithm
#QGIS #FOSS4G

[@BNHRdotXYZ]

[As of March 15, 2022 with QGIS 3.16++ on Windows] If you are using QGIS on Windows and utilizing Virtual Layers on the DB Manager to do the query above and nothing happens when you click Execute, it might be this issue where the geometry field does not appear on Virtual Layers: facebook.com/bnhr.xyz/posts/1051311215729359 It's a fairly new issue (late 2021) and mostly affects QGIS versions installed on Windows 10 using the OSGeo4W installers. It's not on Linux (which I run).

[@kadalijo8815]

is it possible to perform the query using python?how to access the dbmanager using python?

[@franciscojoseromerafernand2298]

Hello, thank you very much for the video. I am trying to do the same (remove duplicates) but not from geometries but from lines. The idea is to eliminate the dividing walls of the buildings. Is there a way to adapt the code to make this selection? Thank you very much in advance.

[@yannikwohnsdorf8944]

Hey, this might be too late for you but the same code works with lines/polylines as well since both lines and polygons have the geometry attribute.

[@benciusilviustefan2879]

How can I create the field "num_geom" with the number of duplicates of the same geometry?

[@BNHRdotXYZ]

Hi! It automatically gets created using the SQL query shown in the video. You can read the full post here: bnhr.xyz/2020/12/09/select-duplicate-geometries-layer-qgis.html