create type emp2_oty is object 
(
 empno  number,ename  varchar2(20),deptno number
);

create type emp2_nt is table of emp2_oty;

和

type emp2_oty is record
(
 empno  number,deptno number
);

create type emp2_nt is table of emp2_oty;

请详细说明。