On Thu, Dec 21, 2006 at 11:43:27AM -0500, Tom Lane wrote: > Andrew Dunstan <[EMAIL PROTECTED]> writes: > > Tom Lane wrote: > >> You could make a case that we need *three* numbers: a permanent column > >> ID, a display position, and a storage position. > > > Could this not be handled by some catalog fixup after an add/drop? If we > > get the having 3 numbers you will almost have me convinced that this > > might be too complicated after all. > > Actually, the more I think about it the more I think that 3 numbers > might be the answer. 99% of the code would use only the permanent ID. > Display position would be used in *exactly* one place, namely while > expanding "SELECT foo.*" --- I can't think of any other part of the > backend that would care about it. (Obviously, client-side code such > as psql's \d would use it too.) Use of storage position could be > localized into a few low-level tuple access functions, probably. > > The problems we've been having with the concept stem precisely from > trying to misuse either display or storage position as a permanent ID. > That's fine as long as it actually is permanent, but as soon as you > want to change it then you have problems. We should all understand > this perfectly well from a database theory standpoint: pg_attribute > has to have a persistent primary key. (attrelid, attnum) is that key, > and we can't go around altering a column's attnum without creating > problems for ourselves.
Is there enough consensus on this to add it to the TODO? -- Jim Nasby [EMAIL PROTECTED] EnterpriseDB http://enterprisedb.com 512.569.9461 (cell) ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq