Re: conditional dropping of columns/constraints

robertmhaas(at)gmail(dot)com (Robert Haas) writes:
> On Mon, May 4, 2009 at 10:10 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> Would a patch adding 'IF EXISTS' support to:
>> - ALTER TABLE ... DROP COLUMN
>> - ALTER TABLE ... DROP CONSTRAINT
>> possibly be accepted?
>>
>> Having it makes the annoying task of writing/testing of schema-upgrade
>> scripts a bit easier.
>
> 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 ...
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