Querying distinct values in a DFF value set with validation type as Table

Summary:

Can someone help please? Our concern is that we're using a Table Validation type for our value set in one of our DFFs and we're not getting any distinct values. In BIP SQL, we can insert in the select statement the word 'distinct'. How can we do the same in a Value Set?

Content (please ensure you mask any confidential information):

FROM Clause: egp_categories_tl mc, egp_item_categories mic, egp_category_sets_tl mcs

Value Column Name: SUBSTR(MC.CATEGORY_NAME, 1, 150)
Value Column Type: VARCHAR2
Value Column Length: 150

WHERE Clause:
mcs.category_set_id = mic.category_set_id