In a SQL Server database, can you create multiple foreign keys on a table and all the column involved have some null values? If the table already has a primary key and you need to create foreign keys, do you have to make the new column the primary key in order to create a foreign key? Do you have some examples or illustrations (T-SQL Syntax) on how to create multiple foreign keys on two tables as a unique constraint while some of the values in these new foreign keys will have some null values?