Re: conditional dropping of columns/constraints

Hi Chris,

On 05/04/2009 09:21 PM, Chris Browne wrote:
> robertmhaas@gmail.com (Robert Haas) writes:
>> On Mon, May 4, 2009 at 10:10 AM, Andres Freund<andres@anarazel.de>  wrote:
>>> Would a patch adding 'IF EXISTS' support to:
>>> - ALTER TABLE ... DROP COLUMN
>>> - ALTER TABLE ... DROP CONSTRAINT
>>> possibly be accepted?
>> Can't speak for the committers, but I've wished for this a time or two myself.
> For constraints, it's easy enough to treat that as idempotent; it's no
> big deal to drop and re-add a constraint.
>
> For columns, I'd *much* more frequently be interested in
>     ALTER TABLE ... ADD COLUMN IF NOT EXISTS ...
>
> Note that this is distinctly NOT the same as:
>     ALTER TABLE ... DROP COLUMN IF EXISTS ...
>     ALTER TABLE ... ADD COLUMN ...
Yes, I would like to have that myself - but this seems to open a way 
much bigger can of worms.
Also the problem solved by both suggestions are not completely congruent 
- so I thought better tackle the easier one first before starting a long 
and arduous discussion...

Andres