Re: PERIOD foreign key feature - Mailing list pgsql-hackers
| From | David G. Johnston |
|---|---|
| Subject | Re: PERIOD foreign key feature |
| Date | |
| Msg-id | CAKFQuwZZObJj964eRkw6=kEEA3S_WQiz4Z+r4kk_yEaH9-r_tw@mail.gmail.com Whole thread Raw |
| In response to | PERIOD foreign key feature (Bruce Momjian <bruce@momjian.us>) |
| Responses |
Re: PERIOD foreign key feature
|
| List | pgsql-hackers |
On Tue, May 7, 2024 at 7:54 AM Bruce Momjian <bruce@momjian.us> wrote:
In this commit:
commit 34768ee3616
Author: Peter Eisentraut <peter@eisentraut.org>
Date: Sun Mar 24 07:37:13 2024 +0100
Add temporal FOREIGN KEY contraints
Add PERIOD clause to foreign key constraint definitions. This is
supported for range and multirange types. Temporal foreign keys check
for range containment instead of equality.
This feature matches the behavior of the SQL standard temporal foreign
keys, but it works on PostgreSQL's native ranges instead of SQL's
"periods", which don't exist in PostgreSQL (yet).
Reference actions ON {UPDATE,DELETE} {CASCADE,SET NULL,SET DEFAULT}
are not supported yet.
Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: jian he <jian.universality@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+renyUApHgSZF9-nd-a0+OPGharLQLO=mDHcY4_qQ0+noCUVg@mail.gmail.com
this text was added to create_table.sgml:
In addition, the referenced table must have a primary
key or unique constraint declared with <literal>WITHOUT
--> OVERLAPS</literal>. Finally, if one side of the foreign key
--> uses <literal>PERIOD</literal>, the other side must too. If the
<replaceable class="parameter">refcolumn</replaceable> list is
omitted, the <literal>WITHOUT OVERLAPS</literal> part of the
primary key is treated as if marked with <literal>PERIOD</literal>.
In the two marked lines, it says "if one side of the foreign key uses
PERIOD, the other side must too." However, looking at the example
queries, it seems like if the foreign side has PERIOD, the primary side
must have WITHOUT OVERLAPS, not PERIOD.
Does this doc text need correcting?
The text is factually correct, though a bit hard to parse.
"the other side" refers to the part after "REFERENCES":
FOREIGN KEY ( column_name [, ... ] [, PERIOD column_name ] ) REFERENCES reftable [ ( refcolumn [, ... ] [, PERIOD column_name ] ) ]
***(shouldn't the second occurrence be [, PERIOD refcolum] ?)
The text is pointing out that since the refcolumn specification is optional you may very well not see a second PERIOD keyword in the clause. Instead it will be inferred from the PK.
Maybe:
Finally, if the foreign key has a PERIOD column_name specification the corresponding refcolumn, if present, must also be marked PERIOD. If the refcolumn clause is omitted, and thus the reftable's primary key constraint chosen, the primary key must have its final column marked WITHOUT OVERLAPS.
David J.
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