Hiding duplicates from dropdown when using value relation in QGIS Form

Question

I've got a vector layer with a QGIS Form and the column "test" in the attribute table. I have values for the columns e.g: abc, abc, abcd.

I defined a form for this Layer. The type for the column "test" is Value Relation and I checked Use Completer.

When I create a new feature for this Layer in the form I get a dropdown when I type the first letter as desired. But in the dropdown, I have three options to select: abc, abc, abcd. So abc is duplicated.

I would like to remove the duplicates from this list. I just would like to see: abc, abcd

Is there a possibility to do this?

QGIS-Version: 3.22.9

How-To-Reproduce:

1. Open an empty Project
2. Create an empty shape-layer with one text field
3. In Form use Value Relation and check Use Completer
4. Add a new feature

Answer 1

You can use the Value Map form widget to have a list of unique items, even from a field with duplicate values.

From the documentation :

Value Map: A combo box with predefined items. The value is stored in the attribute, the description is shown in the combo box. You can define values manually or load them from a layer or a CSV file.

Answer 2

The answer by @J.Monticolo should be correct. Additionally, your data may be the source of the problem if there are blank spaces hidden in the values. For example, your values may include 'abc', ' abc', 'abc ', or ' abc '.

These often arise as data entry errors and are difficult to visually spot. They will appear separately in a value map, but because the blank spaces are difficult to notice they will appear to be duplicated.

Answer 3

"fid" = array_first(array_agg("fid", group_by:="Direction"))