> What is uniqueidentifier as a data type?

> Also what is the data type for setting unique STRINGS ((nchar,
> nvarchar), for example to be used for emails and user names in a user
> registration system).
>
> SQL Server does not allow me set primary keys for columns where data
> types are not INT.

Erland Sommarskog wrote:
> Dot Net Daddy (cagriandac@gmail.com) writes:
> > What is uniqueidentifier as a data type?
>
> A uniqueidentifier is a 128-bit value, which is generated in such a way
> that it is guaranteed to be unique in the whole universe. (Well, at least
> this planet.) They are not specific to SQL Server, but Windows has them
> all over the place, but calls them GUIDs.
>
> > Also what is the data type for setting unique STRINGS ((nchar,
> > nvarchar), for example to be used for emails and user names in a user
> > registration system).
> >
> > SQL Server does not allow me set primary keys for columns where data
> > types are not INT.
>
> Huh? You can use almost any data type for primary keys. Since a primary
> key is an index, the total key size may not execeed 900 bytes, so you
> cannot use things like text or nvarchar(MAX).
>
>
> --
> Erland Sommarskog, SQL Server MVP, esquel@sommarskog.se
>
> Books Online for SQL Server 2005 at
> http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx
> Books Online for SQL Server 2000 at
> http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx