Using CASE statements to sort multiple values in QGIS Field Calculator

Question

I am working with land use data in QGIS and have multiple values in a field (let's call the field "zoning") that I would like to categorize into a broader parent field called "land_use". So, there are multiple values in the "zoning" field that can result in one value in the new "land_use" field. For instance, values "A1", "A2" and "E" in the "zoning" field should be labelled as "Residential" in the new "land_use" field. I also have many other values in the zoning field that I need to recategorize into the land use field and would like to do this using one expression if possible (e.g., "CO1" or "CEW" as "Commercial", etc.).

Following another thread, I wrote this code:

CASE
 WHEN "stat_land_" = 'A1' OR "stat_land_" = 'A2' OR "stat_land_" = 'A9' OR "stat_land_" = 'E' OR "stat_land_" = 'E2'
 THEN 'Residential|'
END
||
CASE
 WHEN "stat_land_" = 'C' OR "stat_land_" = 'C1'
 THEN 'Vacant Land|'
END
||
CASE
 WHEN "stat_land_" = 'D1' OR "stat_land_" = 'D2' OR "stat_land_" = 'D3' OR "stat_land_" = 'E1' OR "stat_land_" = 'E3'
 THEN 'Agriculture|'
END
||
CASE
 WHEN "stat_land_" = 'C04'
 THEN 'Commercial|'
 ELSE 'Other'
END 

However, all my values end up in NULL. What am I doing wrong?

Answer 1

Use like this:

CASE
 WHEN "stat_land_" IN ('A1', 'A2', 'A9', 'E', 'E2')
 THEN 'Residential' 
 
 WHEN "stat_land_" IN ('C', 'C1')
 THEN 'Vacant Land'
 
 WHEN "stat_land_" IN ('D1', 'D2', 'D3', 'E1', 'E3')
 THEN 'Agriculture'
 
 WHEN "stat_land_" = 'C04'
 THEN 'Commercial'
 
 ELSE 'Other'
 
END 

The problem is probably about operator ||.

operator ||

Joins two values together into a string.
If one of the values is NULL the result will be NULL. See the CONCAT function for a different behavior.

• pigreco: to avoid typing the field name multiple times, you can use the IN operator: ``` CASE WHEN "stat_land_" IN ('A1', 'A2', 'A9', 'E', 'E2') THEN 'Residential' WHEN "stat_land_" IN ('C', 'C1') THEN 'Vacant Land' WHEN "stat_land_" IN ('D1', 'D2', 'D3', 'E1', 'E3') THEN 'Agriculture' WHEN "stat_land_" = 'C04' THEN 'Commercial' ELSE 'Other' END ```