求高人解答一下为什么日期可以直接insert string格式，不需要转成datetime格式？

insert ignore into actor 
values (1, "PENELOPE", "GUINESS", "2006-02-15 12:34:33"),
       (2, "NICK", "WAHLBERG", "2006-02-15 12:34:33")

以下转成datetime格式也能跑。

insert ignore into actor 
values (1, "PENELOPE", "GUINESS", str_to_date("2006-02-15 12:34:33", "%Y-%m-%d %H:%i:%s")),
       (2, "NICK", "WAHLBERG", str_to_date("2006-02-15 12:34:33", "%Y-%m-%d %H:%i:%s"))