cmcklw -

There has to be some element that matches what you're importing to what's already in there. Meaning - there would need to be some way for you to say on a row-by-row basis, that this row from this table matches up with THIS row in this other table. Without having some basis to be able to cross-reference them, how could you figure that out?

Whether it's an identity field, a name field, etc... or several fields really isn't important, but that "natural key" (interestingly enough - there's a bit of a brawl going on on another thread about "natural keys") would be what you need to code into the condition. Meaning - is there or is there NOT a match? And if this is a mismatch anywhere in that natural key, then that would entail a NEW row versus updating an existing row with new data.