Yes, for primary index you need a database. BUT "candidate" indexes also prevent duplicates and can be used with free tables + any number of tags.
You could also add your free table to a database with "add table" command.
Cetin

>Thanks first.
>I am using a free table and I know if I am using a database, I can assign a primary key to that table, right? But now can I add this primary key to my free table if I don't have a database? Or I can change it to a database?
>Anyway, I am trying to use SEEK() for my purpose.
>>>Dear all,
>>>
>>>I have a table. When the user adds a new record, I want to check if this new record (for example, same UserID) has already exist in the table or not. How can I do that?
>>>I found in an example that it has a "Save" button and the CLICK event is:
>>>result = TABLEUPDATE(.F.) if result = .F. =MESSAGEBOX("Fail to save!"+CHR(13)+"User ID already exists";
>>>else
>>>....
>>>...
>>>It works in this example. I have tried to find any coding for checking about the existing data in this example but cannot find any idea.
>>>Anyone can help?
>>>
>>>Thanks
>>>Power
>>
>>

---

Power,
>>Probably sample depends on table's primary key. If UserId is primary field than tableupdate(.f.) would return .f.
>>If you don't do that with a primary key you could use other workarounds :
>>-If row buffered use the table again and seek userid in "used again" alias (use again doesn't see buffered ones).
>>-Do the same with an SQL check (it doesn't see buffered also).
>>-Also you could just use seek (lookup()). Seek would catch first entered and if its recno() # yours than its duplicate.
>>Cetin