>>>If the index is PK index you need to drop constraint not index.
>>
>>Until now I haven't used PK except when I have an autoincrement field. What is the advantage of a PK other than assurance of uniqueness? Are there performance gains?
>
>If you want to create proper normalized design for your database, then you need to create primary key in every table.
>
>Please take a moment to read this blog post
>http://blogs.lessthandot.com/index.php/DataMgmt/DBProgramming/best-practice-every-table-should-have-a

What I meant to say was is that we do use primary keys in all tables, but we don't mark them as PK constraint in the SQL Server database. I was wondering what gain there is to have that constraint.