Merging multiple shapefiles and finding which shapefile gives the minimum value for each attribute in QGIS?

Question

I have several different shapefiles that I want to combine into one based on the minimum value of each attribute. I found this solution. However, I also want to know which shapefile each minimum value came from.
For example, I have 5 shapefiles with values in each one of 10 attributes. For each attribute, I found the minimum value from one of the 5 shapefiles using the method in the solution above. But I also want to know which of the 5 shapefiles the minimum value came from for each attribute. Is this possible?

H. Cahill · Accepted Answer

I found the answer to my question here.
I use "select" to choose which columns (in this case, "layer") I want to keep:
select layer, min(id), "geometry" from Merged group by attribute

Here, "layer" is a column in my Attribute Table with information about which shapefile each "id" came from.

Merging multiple shapefiles and finding which shapefile gives the minimum value for each attribute in QGIS?

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