Re: ON CONFLICT and WHERE

On Mon, Nov 14, 2022 at 2:55 AM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> On 11/13/22 13:07, Tom Lane wrote:
> > Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
> >> INSERT INTO books VALUES (12, 0, CURRENT_TIMESTAMP)
> >> ON CONFLICT (id)
> >> WHERE updated IS NULL OR updated + INTERVAL '2min' < CURRENT_TIMESTAMP
> >> DO UPDATE
> >> SET version = books.version + 1, updated = CURRENT_TIMESTAMP;
> >
> >> I have not used WHERE with ON CONFLICT myself so it took longer then I
> >> care to admit to correct the above to:
> >
> >> INSERT INTO books VALUES (12, 0, CURRENT_TIMESTAMP)
> >> ON CONFLICT (id)
> >> DO UPDATE
> >> SET version = books.version + 1, updated = CURRENT_TIMESTAMP
> >> WHERE books.version IS NULL OR books.updated + INTERVAL '2min' <
> >> CURRENT_TIMESTAMP;
> >
> >> The question is why did the first case just ignore the WHERE instead of
> >> throwing a syntax error?
> >
> > A WHERE placed there is an index_predicate attachment to the ON CONFLICT
> > clause. It doesn't have any run-time effect other than to allow partial
> > indexes to be chosen as arbiter indexes. TFM explains
> >
> > index_predicate
> >
> > Used to allow inference of partial unique indexes. Any indexes
> > that satisfy the predicate (which need not actually be partial
> > indexes) can be inferred.
> >
> > This strikes me as a bit of a foot-gun. I wonder if we should make
> > it safer by insisting that the resolved index be partial when there's
> > a WHERE clause here. (This documentation text is about as clear as
> > mud, too. What does "inferred" mean here? I think it means "chosen as
> > arbiter index", but maybe I misunderstand.)
>
> Alright I see how another use of WHERE comes into play.
>
> I do agree with the clarity of the description, especially after looking
> at the example:
>
> "
> Insert new distributor if possible; otherwise DO NOTHING. Example
> assumes a unique index has been defined that constrains values appearing
> in the did column on a subset of rows where the is_active Boolean column
> evaluates to true:
>
> -- This statement could infer a partial unique index on "did"
> -- with a predicate of "WHERE is_active", but it could also
> -- just use a regular unique constraint on "did"
> INSERT INTO distributors (did, dname) VALUES (10, 'Conrad International')
> ON CONFLICT (did) WHERE is_active DO NOTHING;
> "
>
> I honestly cannot figure out what that is saying.
>
> >
> > regards, tom lane
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com
>
>
>
>
INSERT INTO books VALUES (12, 0, CURRENT_TIMESTAMP)
ON CONFLICT (id)
WHERE version IS NULL OR updated + INTERVAL '2min' < CURRENT_TIMESTAMP
DO UPDATE
SET version = books.version + 1, updated = CURRENT_TIMESTAMP;

Since id is already the primary key, it skipped the WHERE part. it resolves
to the DO UPDATE part.

from test code.

> create table insertconflicttest(key int4, fruit text);
> create unique index partial_key_index on insertconflicttest(key) where
> fruit like '%berry';
>

In this case, the on conflict clause should be exactly like *on conflict
(key) where fruit like '%berry'*

-- fails
insert into insertconflicttest values (23, 'Blackberry') on conflict (key)
do update set fruit = excluded.fruit;
ERROR: there is no unique or exclusion constraint matching the ON CONFLICT
specification
insert into insertconflicttest values (23, 'Blackberry') on conflict (key)
where fruit like '%berry' or fruit = 'consequential' do nothing;
ERROR: there is no unique or exclusion constraint matching the ON CONFLICT
specification
insert into insertconflicttest values (23, 'Blackberry') on conflict
(fruit) where fruit like '%berry' do update set fruit = excluded.fruit;
ERROR: there is no unique or exclusion constraint matching the ON CONFLICT
specification

--
I recommend David Deutsch's <<The Beginning of Infinity>>

Jian