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.
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
