Delete a
To delete a unique constraint
-or-
Open the Table Designer for the table containing the constraint, right-click in the Table Designer, and choose Indexes/Keys from the shortcut menu.
Caution Choosing Delete will result in an action that cannot be undone without losing all other changes made to the database diagram. To undo this action, close this database diagram or table design window and all other open database diagrams and table design windows without saving the changes.
The constraint is deleted from the database when you save the table or diagram.
Constraints | Creating a Unique Constraint | Unique Constraints