Re: [BUGS] BUG #14827: "ALTER TABLE... IF NOT EXISTS...ADD..BIGSERIAL" leaves extra sequences

On Tue, Sep 26, 2017 at 4:57 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

I tried to address only the ALTER TABLE ... ADD COLUMN IF NOT EXISTS statement, and do not touch CREATE TABLE statements...

For example when we add a new SERIAL column to a relation:

ALTER TABLE foo ADD COLUMN bar SERIAL;

What I understood is actually PostgreSQL will convert it to:

1. CREATE SEQUENCE foo_bar_seq;

2. ALTER TABLE foo ADD COLUMN bar INTEGER DEFAULT nextval('foo_bar_seq');

3. ALTER SEQUENCE foo_bar_seq OWNER BY foo.bar;

> I don't feel like this is exactly a "must fix" problem, and it certainly
> isn't one that we should fix by introducing different oddities of
> behavior.
>

When I see the code I felt the same... :-(

>  I'm also

> not clear on how to document it.  The documentation right now is quite
> clear, and accurate, about what SERIAL does:
> https://www.postgresql.org/docs/devel/static/datatype-numeric.html#datatype-serial
> This patch falsifies that, and so would any other conditional creation
> of the sequence.
>

This patch doesn't falsifies that, because will act just when IF NOT EXISTS is used...