Horton

Re: SQL:2011 application time

Paul A Jungwirth <pj@illuminatedcomputing.com>

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From: Paul Jungwirth <pj@illuminatedcomputing.com>
To: Vik Fearing <vik@postgresfriends.org>, Peter Eisentraut <peter@eisentraut.org>
Cc: Corey Huinker <corey.huinker@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-09-01T19:56:40Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Rename gist stratnum support function

  2. Remove support for temporal RESTRICT foreign keys

  3. Cache NO ACTION foreign keys separately from RESTRICT foreign keys

  4. Fix NO ACTION temporal foreign keys when the referenced endpoints change

  5. Improve whitespace in without_overlaps test

  6. Tests for logical replication with temporal keys

  7. Support for GiST in get_equal_strategy_number()

  8. Make the conditions in IsIndexUsableForReplicaIdentityFull() more explicit

  9. Replace get_equal_strategy_number_for_am() by get_equal_strategy_number()

  10. Improve internal logical replication error for missing equality strategy

  11. Simplify IsIndexUsableForReplicaIdentityFull()

  12. Fix ALTER TABLE / REPLICA IDENTITY for temporal tables

  13. doc: Update pg_constraint.conexclop docs for WITHOUT OVERLAPS

  14. doc: Add PERIOD to ALTER TABLE reference docs

  15. doc: Add WITHOUT OVERLAPS to ALTER TABLE reference docs

  16. Add temporal FOREIGN KEY contraints

  17. Add temporal PRIMARY KEY and UNIQUE constraints

  18. Add stratnum GiST support function

  19. Avoid crashing when a JIT-inlined backend function throws an error.

  20. Revert temporal primary keys and foreign keys

  21. Fix ON CONFLICT DO NOTHING/UPDATE for temporal indexes

  22. Add test for REPLICA IDENTITY with a temporal key

  23. Use half-open interval notation in without_overlaps tests

  24. Use daterange and YMD in without_overlaps tests instead of tsrange.

  25. Rename pg_constraint.conwithoutoverlaps to conperiod

  26. Fix comment on gist_stratnum_btree

  27. Add missing TAP test name

  28. Improve error handling of HMAC computations

  29. Rename functions to avoid future conflicts

On 9/1/23 03:50, Vik Fearing wrote:
> On 9/1/23 11:30, Peter Eisentraut wrote:
>> 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.
> 
> I prefer the first option.  That is: WITHOUT OVERLAPS applies only to 
> the column or expression it is attached to, and need not be last in line.

I agree. The second option seems confusing and is more restrictive.

I think allowing multiple uses of `WITHOUT OVERLAPS` (and in any 
position) is a great recommendation that enables a lot of new 
functionality. Several books[1,2] about temporal databases describe a 
multi-dimensional temporal space (even beyond application time vs. 
system time), and the standard is pretty disappointing here. It's not a 
weird idea.

But I just want to be explicit that this isn't something the standard 
describes. (I think everyone in the conversation so far understands 
that.) So far I've tried to be pretty scrupulous about following 
SQL:2011, although personally I'd rather see Postgres support this 
functionality. And it's not like it goes *against* what the standard 
says. But if there are any objections, I'd love to hear them before 
putting in the work. :-)

If we allow multiple+anywhere WITHOUT OVERLAPS in PRIMARY KEY & UNIQUE 
constraints, then surely we also allow multiple+anywhere PERIOD in 
FOREIGN KEY constraints too. (I guess the standard switched keywords 
because a FK is more like "MUST OVERLAPS". :-)

Also if you have multiple application-time dimensions we probably need 
to allow multiple FOR PORTION OF clauses. I think the syntax would be:

UPDATE t
   FOR PORTION OF valid_at FROM ... TO ...
   FOR PORTION OF asserted_at FROM ... TO ...
   [...]
   SET foo = bar

Does that sound okay?

I don't quite understand this part:

 >> Also, your implementation
 >> requires at least one non-overlaps column, which also seems like a
 >> confusing restriction.

That's just a regular non-temporal constraint. Right? If I'm missing 
something let me know.

[1] C. J. Date, Hugh Darwen, Nikos Lorentzos. Time and Relational 
Theory, Second Edition: Temporal Databases in the Relational Model and 
SQL. 2nd edition, 2014.
[2] Tom Johnston. Bitemporal Data: Theory and Practice. 2014.

-- 
Paul              ~{:-)
pj@illuminatedcomputing.com