@Brenden thank you for your answer,
apparently I Want to index pages and not relationship names,
The only current issue is "RightNodeID" column is not searchable using a Pages index.
I'm using the below SQL in the (Smart Search Filter), but whenever I select a value nothing showing in the (Smart search Restults)
"SELECT DISTINCT 'RightNodeID', '(int)' + CONVERT(varchar(10), [DocumentID]), CategoryDisplayName, [DocumentID]
FROM View_CMS_Tree_Joined AS V WITH (NOLOCK, NOEXPAND)
INNER JOIN SiteName_CategoriesPageType AS C WITH (NOLOCK) ON [V].[DocumentForeignKeyValue] = [C].CategoriesPageTypeID AND V.ClassName = N'SiteName.CategoriesPageType'
INNER JOIN [CMS_Relationship] AS D WITH (NOLOCK) ON [V].[DocumentID] = [D].[RightNodeID] AND [RelationshipNameID] = 2"
as I'm new in Kentico and not fully aware of all its classes/methods.
I don't know if anyone already create a custom index includes all of the data from a Pages index and added an additional fields?