공부할 개념

빌더 패턴

https://velog.io/@injoon2019/%EB%94%94%EC%9E%90%EC%9D%B8%ED%8C%A8%ED%84%B4-%EB%B9%8C%EB%8D%94-%ED%8C%A8%ED%84%B4

COUNT(*)와 COUNT(column)의 차이

https://velog.io/@injoon2019/SQL-COUNT%EC%99%80-COUNTcolumn%EC%B0%A8%EC%9D%B4

Collections.emptyList()

https://velog.io/@injoon2019/%EC%9E%90%EB%B0%94-Collections.EMPTYLIST