Primary key or not primary key.........

Hello, i have a paradox table with the first field named 'codice'.
In this field i can find more time the same code (value).
When i create the index   (  Table.AddIndex('', 'codice', [ixPrimary])  ) i
lost many record.
I need to create an index on the first field for each value in thet field .

Can help me?