How to use distinct in the DFF value set query

Summary:

We have a requirement to add Line Manager DFF in the requisition line DFF for approval purpose. To get the unique values i am trying to use the Distinct function in the Value set query.

Issue: In the column name field I have tried to use Distinct SUBSTR(PPNFF.DISPLAY_NAME,1,150) but it throws error.

Later, I found one document as we need to use the distinct in the Where clause (Doc ID 2151045.1).

Used in where clause: ROWID=(select max(ROWID) from PER_PERSON_NAMES_F PPNFF2 where PPNFF2.DISPLAY_NAME = PPNFF.DISPLAY_NAME)

But it is not showing any value, In the DFF it says No data found. Duplicate values coming if I remove the ROWID condition.