| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | jian he <jian(dot)universality(at)gmail(dot)com> |
| Cc: | pgsql-general list <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: explicit-locking.html "key values" reference |
| Date: | 2023-05-27 03:20:31 |
| Message-ID: | CAKFQuwbEFuHrg0QvmPBOM-BpewVVnNomx8DVqZWLdgF+Auc5hg@mail.gmail.com |
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| Lists: | pgsql-general |
On Fri, May 26, 2023 at 8:02 PM jian he <jian(dot)universality(at)gmail(dot)com> wrote:
>
> I still feel confused about "the key values".
>
The "key" here is the Foreign Key relationship. In short, FOR NO KEY
UPDATE, promises that PK/FK values on the table will not be changed. Only
non-FK/PK columns can be changed. In neither case may the row be removed
either since that would necessitate changing the key to "non-existent".
However, the "UPDATE" part basically means "I am going to update some other
column". On the KEY SHARE side you basically get "I only care that this
row/relationship continues to exist, you may change other attributes".
David J.
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