Developers delete a primary key constraint when they want to remove the requirement for uniqueness for the values entered in a column or a combination or columns.
1. In Object Explorer, right-click the table with the primary key, and click Design (Modify in SP1 or earlier).
The table opens in Table Designer.
2. In the table grid, right-click the row with the primary key and choose Remove Primary Key to toggle the setting from on to off.
The constraint is deleted from the database when developers save the table or diagram.