How to change reference to another table in PostgreSQL?

Question

PostgreSQL

Hello!
I have a table with columns:

create table  app_public.category (
    id uuid primary key default gen_random_uuid(),
    parent_id uuid default null
);

how do i change the parent_id column to the following value:

parent_id uuid references app_public.category on delete cascade

?
This column is currently empty, so there is no need to save the old values..

Answer 1

ALTER TABLE app_public.category
ADD CONSTRAINT blah
FOREIGN KEY (parent_id) references app_public.category (id)
on delete cascade;

Or DROP COLUMN + ADD COLUMN