Re: INSERT ... ON CONFLICT {UPDATE | IGNORE}

On Mon, Sep 29, 2014 at 1:40 PM, Kevin Grittner <kgrittn@ymail.com> wrote:
> I think that the subset of the MERGE syntax that would be needed
> for UPSERT behavior would be as follows.  For one row as literals:
>
>   MERGE INTO tab t
>     USING (VALUES ('foo', 'p1')) new(id, colB)
>     ON (t.id = new.id)
>     WHEN MATCHED THEN
>       UPDATE SET colB = new.colB
>     WHEN NOT MATCHED THEN
>       INSERT (id, colB) VALUES (new.id, new.colB);
>
> If you have a bunch of rows in a "bar" table you want to merge in:
>
>   MERGE INTO tab t
>     USING (SELECT id, colB FROM bar) b
>     ON (t.id = b.id)
>     WHEN MATCHED THEN
>       UPDATE SET colB = b.colB
>     WHEN NOT MATCHED THEN
>       INSERT (id, colB) VALUES (b.id, b.colB);
>
> I fail to see how this is harder or more problematic than the
> nonstandard suggestions that have been floated.  I don't know why
> we would be even *considering* a nonstandard syntax rather than
> saying that only this subset is supported *so far*.

Heikki, Andres and I are against using MERGE for this, fwiw. Tom
seemed to think so too, on previous occasions. It isn't a matter of
alternative syntaxes. I have described in detail why I think it's a
bad idea - I have linked to that about 3 times in this thread. It
paints us into a corner when we go to make this do what MERGE is
supposed to do. Do you want a feature that, when fully generalized,
plays a special visibility game based on whether or not some exact set
of conditions are met? That is a non-starter, IMV.

The whole idea of using an arbitrary join syntax seems great, but I
need something that works backwards from would-be unique violations.
That's the only way to preserve the UPSERT guarantees (atomicity,
definite insert or update).

-- 
Peter Geoghegan