MtM

aaa.sql

CREATE TABLE user_friend (
  id         BIGSERIAL    NOT NULL,
  user_id    BIGINT       NOT NULL,
  friend_id  BIGINT       NOT NULL,
  created_at TIMESTAMP(0) NOT NULL DEFAULT now(),

  CONSTRAINT pk_user_friend_id PRIMARY KEY (id),
  CONSTRAINT fk_user_friend_user_id FOREIGN KEY (user_id) REFERENCES "user" (id) ON DELETE CASCADE,
  UNIQUE(user_id, friend_id),
  CONSTRAINT not_equal_id CHECK (user_id != friend_id)
);

ALTER TABLE user_friend
  owner TO app;