How to use decode in where clause ?

select 
       emp.empno
      ,emp.ename
      ,emp.deptno
      ,dept.deptno
      ,dept.dname 
from  emp
     ,dept
where emp.deptno=dept.deptno
  and (decode(emp.deptno,10,'ACCOUNTING')=dept.dname
      or
       decode(emp.deptno,20,'RESEARCH')=dept.dname
      or
       decode(emp.deptno,30,'SALES','OPERATIONS')=dept.dname);