I'm trying to dissolve the fields "Inundation" and "EVC_BCS" (to get the areas of inundation and non-inundation for each rarity category). When I do the dissolve, I would also like to sum the field "AREASQM" as well.
I've tried using the Plugin "Dissolve with stats", but I've realised that I can only dissolve by one field (not two).
Thus, I'm quite stuck. How can I dissolve based on two fields whilst summing the "AREASQM" field?
Use Menu Processing / Toolbox / Aggregate, where you can set detailed conditions for
For both, the full power of QGIS expressions can be used to generate complex conditions using multiple attributes.
There is a possibility using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer...
Let's assume there is a polygon layer called 'grid_test' (red squares).
With the following query, it is possible to dissolve two fields while summing a third field.
SELECT GROUP_CONCAT("id") AS ids,
SUM("AREASQM") AS SUM_AREASQM,
ST_union(geometry) AS geom
FROM "grid_test"
GROUP BY "Inundation", "EVC_BCS"
Here the ST_Union() function was used.
The output polygon layer (yellow) with its attribute table will look like
