Re: SQL:2011 application time

On Fri, Mar 22, 2024 at 11:49 PM Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
>
> On 22.03.24 01:35, Paul Jungwirth wrote:
> > > 1. In ri_triggers.c ri_KeysEqual, you swap the order of arguments to
> > ri_AttributesEqual():
> > >
> > > - if (!ri_AttributesEqual(riinfo->ff_eq_oprs[i],
> > RIAttType(rel, attnums[i]),
> > > - oldvalue, newvalue))
> > > + if (!ri_AttributesEqual(eq_opr, RIAttType(rel, attnums[i]),
> > > + newvalue, oldvalue))
> > >
> > > But the declared arguments of ri_AttributesEqual() are oldvalue and
> > newvalue, so passing them
> > > backwards is really confusing. And the change does matter in the tests.
> > >
> > > Can we organize this better?
> >
> > I renamed the params and actually the whole function. All it's doing is
> > execute `oldvalue op newvalue`, casting if necessary. So I changed it to
> > ri_CompareWithCast and added some documentation. In an earlier version
> > of this patch I had a separate function for the PERIOD comparison, but
> > it's just doing the same thing, so I think the best thing is to give the
> > function a more accurate name and use it.
>
> Ok, I see now, and the new explanation is better.
>
> But after reading the comment in the function about collations, I think
> there could be trouble. As long as we are only comparing for equality
> (and we don't support nondeterministic global collations), then we can
> use any collation to compare for equality. But if we are doing
> contained-by, then the collation does matter, so we would need to get
> the actual collation somehow. So as written, this might not always work
> correctly.
>
> I think it would be safer for now if we just kept using the equality
> operation even for temporal foreign keys. If we did that, then in the
> case that you update a key to a new value that is contained by the old
> value, this function would say "not equal" and fire all the checks, even
> though it wouldn't need to. This is kind of similar to the "false
> negatives" that the comment already talks about.
>
> What do you think?
>

we don't need to worry about primary key and foreign key with
different collation.
because it will be error out as incompatible data type,
foreign key constraint will not be created.

if there are the same collation, when we build the query string, we
don't need to worry about collation.
because at runtime, the operator associated oprcode
will fetch collation information later.

main operator and the main oprcode related to this patch(0001, 0002) are:
range_contained_by_multirange
range_eq
range_overlaps
range_contained_by
the first 3 functions will fetch collation information within range_cmp_bounds.
range_contained_by will fetch collation information in
range_contains_elem_internal.

demo:
CREATE COLLATION case_insensitive (provider = icu, locale =
'und-u-ks-level2', deterministic = false);
DROP TABLE IF exists temporal_fk_rng2rng;
DROP TABLE IF exists temporal_rng;
DROP TYPE textrange_case_insensitive;
create type textrange_case_insensitive as range(subtype=text,
collation=case_insensitive);
CREATE TABLE temporal_rng (id int4range, valid_at textrange_case_insensitive);
ALTER TABLE temporal_rng
ADD CONSTRAINT temporal_rng_pk
PRIMARY KEY (id, valid_at WITHOUT OVERLAPS);
CREATE TABLE temporal_fk_rng2rng (
id int4range,
valid_at textrange_case_insensitive,
parent_id int4range,
CONSTRAINT temporal_fk_rng2rng_fk2 FOREIGN KEY (parent_id, PERIOD valid_at)
REFERENCES temporal_rng (id, PERIOD valid_at)
);
INSERT INTO temporal_rng (id, valid_at) VALUES ('[1,2)',
textrange_case_insensitive('c', 'h','[]'));

--fail
INSERT INTO temporal_fk_rng2rng (id, valid_at, parent_id)
VALUES ('[1,2)', textrange_case_insensitive('B', 'B','[]'), '[1,2)');

--fail.
INSERT INTO temporal_fk_rng2rng (id, valid_at, parent_id)
VALUES ('[1,2)', textrange_case_insensitive('a', 'F','[]'), '[1,2)');

--fail.
INSERT INTO temporal_fk_rng2rng (id, valid_at, parent_id)
VALUES ('[1,2)', textrange_case_insensitive('e', 'Z','[]'), '[1,2)');

--ok
INSERT INTO temporal_fk_rng2rng (id, valid_at, parent_id)
VALUES ('[1,2)', textrange_case_insensitive('d', 'F','[]'), '[1,2)');