Modify the foreign key side of a relationship if you want to change which
To modify a foreign key
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Open the Table Designer for the table containing the foreign key you want to modify, right-click in the Table Designer, and choose Properties from the shortcut menu.
Any changes you make to the relationship's properties take effect as soon as you move outside the grid in the property pages. The constraint is updated in the database when you save your table or diagram.
Note Modifying a relationship in a database diagram marks both of the related tables as modified. Consequently, each table will also be marked as modified in any other diagrams in which it appears.
Constraints | Deleting a Foreign Key Constraint | Foreign Key Constraints | Modifying a Primary Key