Occasionally I've seen novel excerpts published in short story venues. They're usually sections of a recent or forthcoming novel that also hold together as a self-contained story. Alternately, sometimes an author starts with the short story, which is later expanded into a novel and sold. (I believe Ender's Game is one such example).
How are these typically handled between the author, the novel publisher, and the short story publisher? Do novel publishers seek out these deals? Do the authors seek them out and then have to "OK" them with the novel publisher?
If I sold an excerpt as a short story, how would that complicate trying to sell the whole novel? If I've already sold the novel, how does that complicate selling the excerpt?
EDIT for clarification (hopefully): If I sell rights to the short story/chapter/excerpt, then go on to try and sell the whole novel (which contains that same bit), are those short story rights likely to conflict with the whole novel rights that the publisher is going to want? If, for example, I sell First North American Serial Rights for the short story, does that also exercise the same rights for the novel containing it?