SQL연습-02DDL,제약조건

CREATE TABLE MEMBER(
  ID VARCHAR2(20) CONSTRAINT MEMBER_ID_PK PRIMARY KEY,
  NAME VARCHAR2(20) CONSTRAINT MEMBER_NAME_NN NOT NULL,
  REGNO VARCHAR2(13) CONSTRAINT MEMBER_REGNO_UK UNIQUE CONSTRAINT MEMBER_REGNO_NN NOT NULL,
  HP VARCHAR2(13) UNIQUE,
  ADDRESS VARCHAR2(100)
  );
  
CREATE TABLE BOOK(
  CODE NUMBER(4) PRIMARY KEY,
  TITLE VARCHAR2(50) NOT NULL,
  COUNT NUMBER(6),
  PRICE NUMBER(10),
  PUBLISH VARCHAR2(50)
  );
 DROP TABLE ORDER2 PURGE; 
CREATE TABLE ORDER2(
  NO VARCHAR2(10),
  ID VARCHAR2(20) CONSTRAINT ORDER2_ID_FK  REFERENCES MEMBER(ID),
  CODE NUMBER(4),
  COUNT NUMBER(6),
  DR_DATE DATE
  );
  
ALTER TABLE ORDER2
  ADD CONSTRAINT ORDER2_ID_PK PRIMARY KEY(NO);
ALTER TABLE ORDER2
  MODIFY CODE CONSTRAINT ORDER2_CODE_NN NOT NULL;
ALTER TABLE ORDER2
  ADD CONSTRAINT ORDER2_CODE_FK FOREIGN KEY(CODE) REFERENCES BOOK(CODE);