After adding one or more columns to a table, you can define the column(s) used for the primary key.
To add a primary key:
Select one or more columns.
Drag the column(s) to the primary key area in the table.
To remove a primary key:
Select the column(s) in the primary key area.
Drag the column(s) from the primary key area to the table's column list.
Note: You can change the primary key name for the table. For more information, see the section called “Modifying Tables” .