I don't see what difference does it make for this discussion.

>I guess we are talking about different things. FK constraint can be done on a key that is a unique in a table, not a PK value. For example, an ASSET NUMBER (equipment ID) has to be unique in the table of assets. But it is not a PK value. Yet, on an order form user has to enter this value of asset number. Then the Asset Number should be saved in the Order table. So user can inadvertently make a mistake and enter the wrong value. I understand that I can programatically check if the value is valid by calling the back end and checking if entered value is in the Asset Table. But I thought that it can be check by the constraint just as well (eliminating double pass to SQL Server). And I see now that most people in this thread do not use this approach.