关于插入date型数据

create table student (name varchar2(10) not null primary key , enrolldate date not null);//创建student表

insert into student values('mark',to_date('08-21-2003','MM-DD-YYYY'));

insert into student values('mark1',to_date('21-08-2003','DD-MM-YYYY'));

insert into student values('mark2','21-8月-2003');

insert into xiongxiaomin.student values('mark3','21-8月-03');

试验第三种和第四种之后发现一点，如果月份为一位数时，前面写上0会报错。