为什么在标识列上出现外键不唯一错误？

Question

If I try to create two tables like this in PostgreSQL 14.3:

CREATE TABLE IF NOT EXISTS foo (
  id INT4 GENERATED BY DEFAULT AS IDENTITY (INCREMENT BY 1 MINVALUE -2147483648 START -2147483648),
  foo TEXT UNIQUE NOT NULL
);

CREATE TABLE IF NOT EXISTS bar (
  id INT4 GENERATED BY DEFAULT AS IDENTITY (INCREMENT BY 1 MINVALUE -2147483648 START -2147483648),
  foo_id INT4 NOT NULL REFERENCES foo(id)
);

I get this output:

$ psql test -f bug01.sql
CREATE TABLE
psql:bug01.sql:9: ERROR:  there is no unique constraint matching given keys for referenced table "foo"

I thought GENERATED BY DEFAULT AS IDENTITY would have satisfied the uniqueness constraint. What am I missing? And how do I resolve the issue?

---

UPDATE: Applying Bergi's answer and comments, I added a primary key constraint to each identity column and that solved the problem:

CREATE TABLE IF NOT EXISTS foo (
  id INT4 PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY (INCREMENT BY 1 MINVALUE -2147483648 START -2147483648),
  foo TEXT UNIQUE NOT NULL
);

CREATE TABLE IF NOT EXISTS bar (
  id INT4 PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY (INCREMENT BY 1 MINVALUE -2147483648 START -2147483648),
  foo_id INT4 NOT NULL REFERENCES foo(id)
);

$ psql test -f bug01.sql
CREATE TABLE
CREATE TABLE

Thanks!

Answer 1

Well, no.GENERATED just means it's harder to overwrite (requiring special syntax) than a DEFAULT value, and AS IDENTITY is just a fancy way of defining an implicit sequence, similar to SERIAL .

You still can insert duplicates in your column, either by resetting the sequence or using OVERRIDING SYSTEM VALUE , you must declare the appropriate constraints to prevent this. Simply make your id the PRIMARY KEY of the table.