Define a Variable List

Define Dept_List = "20,30"

Select *
 From Dept
Where Deptno in (&Dept_list);

old   3:  Where Deptno in (&Dept_list)
new   3:  Where Deptno in (20,30)

   DEPTNO DNAME          LOC
---------- -------------- -------------
       20 RESEARCH       DALLAS
       30 SALES          CHICAGO