On Thu, Oct 27, 2005 at 09:45:05PM -0400, Andrew Dunstan wrote: > > > Jim C. Nasby wrote: > > >Andrew, you mentioned that if you want to change the ordering you should > >just create a new type. What about if you need to change the values that > >are in the enum? MySQL does (or at least did, it's been some time since > >I've messed with this) a horrible job at that. There's no way to rename > >anything; you have to add the new names you want, then do a bulk update, > >then delete the (now old) names. IMO this is broken. > > > > > > > It would just be a standard "ALTER TABLE foo ALTER COLUMN bar TYPE > newtype USING expression" operation. You would write a function that > took a value of the old type and returned a value of the new type and > use a cll to that function in the expression. Since these would be named > types, unlike the case in mysql where they are anonymously defined > inline, this would present no difficulties at all.
But why force a re-write of the entire table just to change the name of something? Or is ALTER COLUMN TYPE smart enough to not touch anything if the mapping function is equality? > >Also, if we are going to maintain ordering and mapping (presumably via > >the internal number that we're storing), then I think we should expose > >that, at least optionally. So for example, you should be able to define > >what a specific enum value means. Not everyone will want a linear > >numbering starting at 0 afterall. > > > > > > What on earth for? Users should not care in the slightest what the > internal representation is . Users who want a map where the values are > exposed should create a lookup table. > > You keep saying that we are using the internal representation as the > ordering. This is simply the wrong way to look at it. The internal > representation REFLECTS the ordering; it doesn't impose it. The user has > imposed the ordering when defining the type. In my enumkit I did provide > a function that gave back the internal representation, but I am not by > any means certain that that's a good idea. Well, someone was arguing that enum should be used as a convenient way to map human labels on a set of values. To me, that means you should be able to define exactly what that set of values is. Personally, I don't see why enum can't just be syntactic sugar on top of a side-table of values and a foreign key. And I guess a view to hide the internals from normal viewing. That would certainly allow the most flexibility, although it probably wouldn't perform as well as what you wrote. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
