Why FOREIGN KEY without CONSTRAINT?

Question

PostgreSQL

Hello!
In general, I create 2 tables and a foreign key from the 2nd to the 1st:

CREATE TABLE tbl_1 (
  id SERIAL PRIMARY KEY
);

CREATE TABLE tbl_2 (
  id     SERIAL PRIMARY KEY,
  tbl_id INT
);
ALTER TABLE tbl_2 ADD CONSTRAINT tbl_2_tbl_1__fk FOREIGN KEY (tbl_id) REFERENCES tbl_1;

I'm trying to insert without an associated entry and I get an error, that's right: Next, I remove the CONSTRAINT and the entry is inserted
INSERT INTO tbl_2 (tbl_id) VALUES (1);

ALTER TABLE tbl_1 DROP CONSTRAINT tbl_1_pkey CASCADE;
INSERT INTO tbl_2 (tbl_id) VALUES (1);

I can’t understand, FOREIGN KEY remains but in fact does nothing (or does it?), Why is it done like that?
Thank you.

Answer 1

FOREIGN KEY is CONSTRAINT tbl_1_pkey
i.e. this team
you deleted FOREIGN KEY