Database tables often have one or more unique indexes defined for various purposes. It may be useful to define a primary key based on an existing index. To view the contents of a unique index in the Primary Key Editor, select Indexes from the Tools menu.
List of unique indexes for the table. To display the associated columns, select an index.
To create or modify a primary key based on a unique index, select an index and select OK. The columns of the unique index replace all previously specified columns in the Key Columns box of the Primary Key Editor.