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I have a polygon layer 'lot' containing an attribute "lot_number". Then, I want to create a Virtual Layer that merges some of the lots while keeping others separated, as the diagram shows below.

Specifically, in the virtual layer, I want to merge the lots with "lot_number" 1, 2 and 4 into one polygon, and ones with "lot_number" 5 and 6 into another polygon. How could I do that?

enter image description here

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I figured this out. First you need to create a new field merged_ID in the lot layer, giving a unique ID to each group of polygons to be merged. The attribute table would look like this:

enter image description here

Then type the following query in the virtual layer creation window:

select st_union(geometry), l.*
from "lot" as l
group by l."merged_ID"
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    When working with a single layer there is no need in an alias i.e. from "lot" as l, simply from "lot"
    – Taras
    Sep 21, 2020 at 5:59

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