Re: Happy column adding (was RE: [HACKERS] Happy column dropping)

At 06:01 PM 1/25/00 -0500, Tom Lane wrote:
>Don Baccus <dhogaza@pacifier.com> writes:
>>> In particular, if parsetrees for stored rules and constraints worked
>>> that way, renumbering attributes that follow the added/dropped column
>>> would become a lot less painful.
>
>> Yes...I see what you're driving at.  Very interesting idea.  The stored
>> rules and constraints would in this case would still refer to the remaining
>> columns after a drop, right?
>
>Right.  You'd still need to scan through all the rules/constraints to
>look for references to a column-to-be-dropped (and then either drop that
>rule/constraint or kick out an error, as appropriate).  But you wouldn't
>have to *change* any surviving rules/constraints, because they'd still
>be referring to the same permanent IDs of the remaining columns.

Good, I understand then.

>Also, inherited ADD COLUMN would become far easier, because it wouldn't
>change the rules/constraints of child tables at all --- even though the
>new column would change the logical numbering of child-table columns,
>it wouldn't change their permanent IDs and thus we wouldn't have to
>update rules/constraints.

Ahhh...yes.  I haven't looked at the inheritance code, yet, but I see
what you're saying.  I think.  Do child-table columns follow parent-table
columns by some chance (in today's absolute column number scheme)?

>If we were willing to hardwire the assumption that DROP COLUMN never
>physically drops a column, but only hides it and adjusts logical column
>numbers, then the physical column numbers could serve as permanent IDs;
>so we'd only need two numbers not three.  This might be good, or not.

Yes.  But if I'm right about how child-table columns are numbered, 
wouldn't add column still cause a problem, i.e. you'd still have to
change their physical column number?

I'm probably misunderstanding here because I've not looked at the 
inheritance mechanism at all.  Maybe I'll do that for a little evening
entertainment.




- Don Baccus, Portland OR <dhogaza@pacifier.com>
  Nature photos, on-line guides, Pacific Northwest
  Rare Bird Alert Service and other goodies at
  http://donb.photo.net.