[DB] 디비 정규화

https://velog.io/@rlrhs11/DB%EB%8D%B0%EC%9D%B4%ED%84%B0%EB%B2%A0%EC%9D%B4%EC%8A%A4%EC%9D%98-%EC%A0%95%EA%B7%9C%ED%99%94%EB%9E%80