Joining CSV tables by multiple attributes

Question

I am using QGIS 3.16

I have a shapefile with an attribute table containing regions, district-numbers and building-numbers and I have an additional table (CSV) that (besides other relevant information) also contains regions, district-numbers and building-numbers. Different regions have different but often also the same district numbers. So region A can have district number 01 and building number 02 and the same is true for region B that can also have district number 01 and building number 02. My CSV table also includes regions, district numbers and building numbers that do not exist in my shapefile and vice versa.

Now I would like to join my shapefile with my CSV table based on all three criteria (region, district number and building number) to have a correct linkage. Cases that are included in the CSV table but do not have corresponding cases in the shapefile shall be listed in the attribute table of the shapefile after the join as well. In the end, I would like to have a shapefile where the attribute table contains:

• The joined information from the CSV table
• Additional cases from the CSV table where there are no corresponding cases in the shapefile (imagine my CSV table also includes region C and XYZ).

Answer 1

After searching for a solution within a group of other GIS-experienced user I found the answer to my question; it is explained in this thread:

QGIS joins 2 FIELDS

So basically you create a new column (data field) in your table (e.g. Excel spreadsheet) and a corresponding one in your attribute table of your shapefile. The newly created column should contain the information of all the columns or fields you want to join. So if you want your join being based on three different columns (A), (B), (C), you can create a column (D) that contains the information of all these columns --> (D) = (A+B+C). Afterwards you just need to join column (D).