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;

A.select * from emp wher sal in (2000,3000);
B.select * from emp wher sal like (2000,3000);
C.select * from emp wher sal = (2000,3000);
D.select * from emp wher sal between 2000 and 3000;