-- https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/ALTER-TABLE.html
CREATE TYPE pet_t AS OBJECT
   (pet_id NUMBER, pet_name VARCHAR2(10), pet_dob DATE);
/
CREATE TYPE pet AS TABLE OF pet_t;
/
CREATE TABLE vet_service (vet_name VARCHAR2(30),
                          client   pet)
  NESTED TABLE client STORE AS client_tab;
ALTER TABLE client_tab ADD UNIQUE (pet_id);