kasukeさんは現在、一生懸命勉強中です

delete from myskills where importance < 0;
insert into myskills (name, level, due, importance) 
  values ('HTML', 1, now(), 10),
  values ('CSS', 1, now(), 10),
  values ('JavaScript', 2, now(), 20);
select * from myskills where due < now();