Re: SQL:2011 application time

On 31.08.23 23:26, Paul Jungwirth wrote:
> I've tried to clean up the first four patches to get them ready for
> committing, since they could get committed before the PERIOD patch. I
> think there is a little more cleanup needed but they should be ready for
> a review.

Looking at the patch 0001 "Add temporal PRIMARY KEY and UNIQUE constraints":

Generally, this looks like a good direction. The patch looks
comprehensive, with documentation and tests, and appears to cover all
the required pieces (client programs, ruleutils, etc.).

I have two conceptual questions that should be clarified before we go
much further:

1) If I write UNIQUE (a, b, c WITHOUT OVERLAPS), does the WITHOUT
OVERLAPS clause attach to the last column, or to the whole column list?
In the SQL standard, you can only have one period and it has to be
listed last, so this question does not arise. But here we are building
a more general facility to then build the SQL facility on top of. So I
think it doesn't make sense that the range column must be last or that
there can only be one. Also, your implementation requires at least one
non-overlaps column, which also seems like a confusing restriction.

I think the WITHOUT OVERLAPS clause should be per-column, so that
something like UNIQUE (a WITHOUT OVERLAPS, b, c WITHOUT OVERLAPS) would
be possible. Then the WITHOUT OVERLAPS clause would directly correspond
to the choice between equality or overlaps operator per column.

An alternative interpretation would be that WITHOUT OVERLAPS applies to
the whole column list, and we would take it to mean, for any range
column, use the overlaps operator, for any non-range column, use the
equals operator. But I think this would be confusing and would prevent
the case of using the equality operator for some ranges and the overlaps
operator for some other ranges in the same key.

2) The logic hinges on get_index_attr_temporal_operator(), to pick the
equality and overlaps operator for each column. For btree indexes, the
strategy numbers are fixed, so this is straightforward. But for gist
indexes, the strategy numbers are more like recommendations. Are we
comfortable with how this works? I mean, we could say, if you want to
be able to take advantage of the WITHOUT OVERLAPS syntax, you have to
use these numbers, otherwise you're on your own. It looks like the gist
strategy numbers are already hardcoded in a number of places, so maybe
that's all okay, but I feel we should be more explicit about this
somewhere, maybe in the documentation, or at least in code comments.

Besides that, some stylistic comments:

* There is a lot of talk about "temporal" in this patch, but this
functionality is more general than temporal. I would prefer to change
this to more neutral terms like "overlaps".

* The field ii_Temporal in IndexInfo doesn't seem necessary and could be
handled via local variables. See [0] for a similar discussion:

[0]:
https://www.postgresql.org/message-id/flat/f84640e3-00d3-5abd-3f41-e6a19d33c40b(at)eisentraut(dot)org

* In gram.y, change withoutOverlapsClause -> without_overlaps_clause for
consistency with the surrounding code.

* No-op assignments like n->without_overlaps = NULL; can be omitted.
(Or you should put them everywhere. But only in some places seems
inconsistent and confusing.)