How do you add a NOT NULL FOREIGN KEY column to an existing (populated) table in MS SQL?

Question

I need to add a NOT NULL column to an existing (populated) table that will be a foreign key to another table. This brings about two problems:

1. When you add the c

Answer 1

Create the column, but allow NULL. Populate the column with the correct data from the foreign key table. Alter the column add not null. Add the foreign key constraint.