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I have a CSV-Layer with multiple columns (e.g. ID, owner_name) and well-known text data to contain information about polygons. One ID can be owned by to owners which would cause the feature to appear twice in the attribute table. I further created a virtual field which concentrates all owners into it.

The code of the virtual field looks like this

concatenate("owner_name" ,group_by:= "ID",concatenator:=', ',order_by:= "owner_name")

This results in a attribute table as follows

ID owner_name all_owners [virtual field]
1 Simon Simon
2 Erica Erica, Peter
2 Peter Erica, Peter
3 Simon Simon

Now I want to the atlas to iterate through all unique values in the all_owners column. In this case:

  1. Simon
  2. Erica, Peter

Important: I do not want to create new (static) layers and use the dissolve function as the data in the "CSV"-Layer might get changed later on and everything shall get updated.

Note: The answer to this similar question (look here) does not work, as Virtual Layers cannot get access to virtual fields as far as I tried.

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What I would do, is create a virtual layer that selects the distinct values of the "all_owners" column and join the geom's to that table. You could then build the atlas on that derivative virtual layer.

This is really doing in qgis with virtual layers what I would do permanently in postgres but I think would work.

I don't work a ton with virtual layers but based on my understanding, they would update automatically when the source data is updated.

This is not pulling from a csv with a virtual column but you should be able to import your csv layer and access your virtual column by name.

The query i just tested was:

enter image description here

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  • Thanks for your answer. However I couldn't make that work: How Do select distinct values from a virtual field? The list of distinct values in the virtual layer would be enough as I can show the features of the original layer using a rule-based style pointing to the "atlas_pagename"
    – gissurfer
    Mar 23 at 15:27
  • start by just select * from my_csv_layer and check that the virtual layer was pulled through and then just switch to selecting distinct column_name
    – Hugh_Kelley
    Mar 23 at 15:30
  • This does not work. I get a promt: "Query preparation error on PRAGMA table_info(_tview): no such column: all_owners" I guess this happens because the virtual layer accesses the original CSV-file (which is not containing the virtual field) and not the imported CSV-layer (which contains the virtual field)
    – gissurfer
    Mar 23 at 15:37
  • are you "adding" the csv file or "importing" the layer
    – Hugh_Kelley
    Mar 23 at 16:57
  • 1
    Can you edit your question to include the code that creates your virtual field? I'd recommend taking this off s/o and joining then emailing [email protected]. you can join here lists.osgeo.org/mailman/listinfo/qgis-user
    – Hugh_Kelley
    Mar 24 at 12:24

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