Uniq cannot be used directly on an ActiveRecord model. 'DISTINCT field' is the...

Uniq cannot be used directly on an ActiveRecord model. 'DISTINCT field' is the only pluck query that translates into the aforementioned SQL

activerecord/lib/active_record/relation/calculations.rb

@@ -135,7 +135,7 @@ def calculate(operation, column_name, options = {})
     #   # SELECT people.id, people.name FROM people
     #   # => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]
     #
-    #   Person.uniq.pluck(:role)
+    #   Person.pluck('DISTINCT role')
     #   # SELECT DISTINCT role FROM people
     #   # => ['admin', 'member', 'guest']
     #