정의된 테이블 예시 테이블 명: article attribute type id (PRIMARY KEY) bigint title varchar content varchar created_at datetime 테이블 명: comment attribute type id (PRIMARY KEY) bigint article_id (FOREIGN KEY) bigint content varchar created_at datetime Subquery SELECT id, title, content, created_at FROM article WHERE created_at < ( SELECT created_at FROM article WHERE id = 1 ); SELECT created_at FROM article WH..