>hello all
>
>i found some records that had the same primary key ID in the table.
>any one can tell me why it happened and how to prevent it?
>

Assignig PRIMARY keys on records is more on end-user responsibility provided that the system have enough validations when inserting new records. What we do is we make separate form which pop-ups to input the ID intended for PRIMARY key whenever the user add records. Upon inputting the ID on the popup window, it seeks the string on the table referencing the PRIMARY key. If FOUND, insertion should be cancelled otherwise, do the necessary insertion. Lot of approaches actually, depending on your taste HOW...