> In short, you have to update every instance of the key, not only in the
> database, but in every application and even in every other
> representation in
> the real world. That could include changing people's bookmarks, notes in
> PDAs,
> even paper reports sitting on people's desks -- a tall order for an SQL
> query.
This also applies to misguided databases that REUSE values from
"auto_increment" columns.
I once had two orders with the same PK value.
One had been mistakenly deleted, then another one took its place, and all
hell broke loose.