Re: BUG #19777: PERIOD foreign key rejects an empty referencing range even though the referenced period covers it

Hi,

On 2026/10/20 18:14, PG Bug reporting form wrote:
>
>
> Expected result: the insert should succeed if an empty referencing period is
> considered covered by the referenced period, consistent with range
> containment and the documented PERIOD foreign-key coverage rule. Please
> confirm whether empty referencing periods are intended to satisfy PERIOD
> foreign keys.

In my opinion, this result is expected because empty is treated
differently by range type and by WITHOUT OVERLAPS constraint.

> SELECT range_agg(p) @> 'empty'::int4range AS parent_covers_empty
> FROM period_parent_minimal
> WHERE k = '[1,2)'::int4range;
>
> The SELECT returns true. Then run:

This is considered to be the same as "select '[0,10)'::int4range @>
'empty';", which returns true since 'empty' range is contained in every
range [1].

[1] https://www.postgresql.org/docs/18/functions-range.html
--
Every range contains the empty range.
--

> INSERT INTO period_child_minimal
> VALUES ('[1,2)'::int4range, 'empty'::int4range);
>
> Actual result: rejected with SQLSTATE 23503 (foreign key violation).

However, the INSERT fails. The point is a WITHOUT OVERLAPS column does
not permit empty range [2]. The referenced table does not permit empty
range so referencing table also cannot accept it.

[2] https://www.postgresql.org/docs/18/sql-createtable.html
--
The `WITHOUT OVERLAPS` column must have a range or multirange type.
Empty ranges/multiranges are not permitted.
--

Regards,
Takeshi Ideriha