Depends on what you want.. If you want to get rid of the duplicates, it would be best to clean up the table.
If you want to stay with the duplicate data and only supress the display, you could freate a view with a group by or a distinct and base your form-block on that view. You could also do the same with a blokc based on a from clause query
Keep your original table - Header
Create new VIew without Duplication. - details
Create Master Details Relationship.
This way you can avoid displaying duplicate records without affecting original table.
We have done this our Employee Management application(Custom)
If you are not clear, you provide your table structure here