You can discard changes in your database diagram that you don’t want to save in the database. For example, if changing a column property in your diagram affects tables that are not represented in your diagram, you may want to abandon the change to avoid making changes to those tables.
To roll back unsaved database changes
Caution Other open diagrams might be affected by your changes even though you closed the diagram without saving it. To be sure that your changes, which still exist in memory, do not affect open diagrams, close all diagrams in your editing session without saving them. If you want to update the database with changes to other diagrams only, save those diagrams before closing the one whose changes you want to discard.