join: 여러개의 표로 분산된 정보를 결합 해 단일한 표로 만드는 것
https://docs.google.com/spreadsheets/d/1OUHAnTPdx0ga8P1_HBm6WUuWs02tvV-31mgi__XmRbc/edit#gid=349905192
https://sql-joins.leopard.in.ua/
https://pearlluck.tistory.com/46
