Delete a table from your database diagram when you want to:
A table that is marked for deletion is permanently deleted from the database when you save your diagram. A reference to that table continues to exist in memory until you save the diagram. If you close the diagram without saving it, the table will continue to exist in your database and appear in your diagram and every other diagram in which it appeared before you marked it for deletion.
To delete a table from the database
Note Deleting a table in a database diagram automatically removes any relationships to it.