Jaime Casanova wrote: > On Thu, Mar 5, 2009 at 10:47 AM, Matteo Beccati <p...@beccati.com> wrote: > >> Guillaume Smet ha scritto: >> >>> On Wed, Mar 4, 2009 at 11:50 AM, Peter Eisentraut <pete...@gmx.net> wrote: >>> >>>> The question is how you want to implement this in a data type independent >>>> fashion. You can't assume that increasing the typmod is a noop for all >>>> data >>>> types. >>>> >>> Sure. See my previous answer on -hackers (I don't think this >>> discussion belong to -bugs) and especially the discussion in the >>> archives about Jonas' patch. >>> >> I recently had a similar problem when I added some domains to the >> application. ALTER TABLE ... TYPE varchar_dom was leading to a full >> table rewrite even though the underlying type definition were exactly >> the same (i.e. varchar(64)). I can live with it, but I suppose this fix >> might be related to the varlen one. >> >> > > ALTER TABLE ... TYPE does cause a table rewrite even if new_type = > old_type, and that is actually useful... > for example when you add a fillfactor to an existing table that > fillfactor will not affect the existing data until you rewrite the > table and a convenient way is exactly using ALTER TABLE ... TYPE. > Well, while this behaviour is well-known for PostgreSQL, this is actually an abuse of syntax. If there are legitimate requirements for rewriting a table, then there should be explicit syntax for such a feature, like "ALTER TABLE ... REWRITE". Rewriting a table in case of "ALTER TABLE ... TYPE" is, by the semantics of that statement, just a side-effect, which may or may not happen, depending on how optimized the DBMS is. It is bad design to avoid optimization just because an unnecessary side-effect would be optimized away. > now, back to the problem... is not easier to define a column as TEXT > and to put a check to constraint the length? if you wanna change the > constraint that will be almost free No. Is it possible to change the column type from VARCHAR(5) to TEXT without a table-rewrite penalty?
ciao, Xuân.
