Subject: Example. Foreign Keys Constraints. Wrong Columns

From: PG Doc comments form <[email-masked]>
Date: Tue, 14 Apr 2026 11:08:35 +0000

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/18/ddl-constraints.html
Description:

https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-FK

In the last example of this section it seems the `users` table is referenced
wrong.

```sql
CREATE TABLE users (
    tenant_id integer REFERENCES tenants ON DELETE CASCADE,
    user_id integer NOT NULL,
    PRIMARY KEY (tenant_id, user_id)
);

CREATE TABLE posts (
    tenant_id integer REFERENCES tenants ON DELETE CASCADE,
    post_id integer NOT NULL,
    author_id integer,
    PRIMARY KEY (tenant_id, post_id),
    FOREIGN KEY (tenant_id, author_id) REFERENCES users ON DELETE SET NULL
(author_id)
);
```

In this example `FOREIGN KEY (tenant_id, author_id) REFERENCES users ON
DELETE SET NULL (author_id)` implies that `users` table columns are named
`(tenant_id, author_id)` but in fact `users` table does not have a
`author_id` column.

That line should be probably like this because `users` tables has a
`user_id` column instead of `author_id`

```sql
CREATE TABLE posts (
    # ...
    FOREIGN KEY (tenant_id, author_id) REFERENCES users (tenant_id, user_id)
ON DELETE SET NULL (author_id)
);
```

---

From: "David G. Johnston" <[email-masked]>
Date: Wed, 15 Apr 2026 08:23:34 -0700

> ON DELETE SET NULL (author_id)

Produce an identical outcome.

The absence of a column list on the former causes the system to look at the
primary key for the named table and use its column list - which is
(tenant_id, user_id), same as the later explicit version.

David J.

---

From: Yushu Chen <[email-masked]>
Date: Fri, 17 Apr 2026 23:06:28 +0800

> (tenant_id, user_id), same as the later explicit version.

Thanks for explanation.

I think "columns mapping" (just how I call it in this example) makes
this example slightly non-intuitive, and reflects a less-common use case.
Would it help to change `author_id` to `user_id` as a more
straightforward case?

Yushu Chen