CREATE TABLE comments (
  id          BIGSERIAL PRIMARY KEY,
  user_id     BIGINT NOT NULL,
  sku         BIGINT NOT NULL,
  text        VARCHAR(255) NOT NULL,
  created_at  TIMESTAMP(3) NOT NULL DEFAULT now()
);

CREATE INDEX ON comments(sku, created_at DESC, user_id ASC);
CREATE INDEX ON comments(user_id, created_at DESC);