A.select * from emp where hiredate>='19820101';
B.select * from emp where hiredate>=to_char('19820101','YYYYMMDD');
C.select * from emp where to_date(hiredate,'YYYYMMDD')>='19820101';
D.select * from emp where to_char(hiredate,'YYYYMMDD')>='19820101';

A.select * from emp where comm='';
B.select * from emp where comm=null;
C.select * from emp where nvl(comm)=0;
D.select * from emp where comm is null;
E.select * from emp where nvl(comm,0)=0;