Mysql 질문입니다

CREATE TABLE `dates` (  `f1` date DEFAULT NULL);INSERT INTO dates (f1) VALUES (CURRENT_DATE());INSERT INTO dates (f1) VALUES (DATE_SUB(CURRENT_DATE(), INTERVAL 1 DAY));INSERT INTO dates (f1) VALUES (DATE_SUB(CURRENT_DATE(), INTERVAL 2 DAY));INSERT INTO dates (f1) VALUES (DATE_SUB(CURRENT_DATE(), INTERVAL 3 DAY));SELECT * FROM dates WHERE f1 < CURRENT_DATE();SELECT * FROM dates WHERE f1 < DATE_SUB(CURRENT_DATE(), INTERVAL 1 DAY);SELECT * FROM dates WHERE f1 < DATE_SUB(CURRENT_DATE(), INTERVAL 2 DAY);SELECT * FROM dates WHERE f1 < DATE_SUB(CURRENT_DATE(), INTERVAL 3 DAY);