SQL> select sum(trunc(sum(sal),-2)) from emp group by deptno;

SUM(TRUNC(SUM(SAL),-2))
-----------------------
                  28900

SQL> ed
Wrote file afiedt.buf

  1  select
  2   (select sum(s) from (select sum(sal) s from emp e where e.deptno=d.deptno group by deptno)) ss
  3* from dept d
SQL> /
 (select sum(s) from (select sum(sal) s from emp e where e.deptno=d.deptno group by deptno)) ss
                                                                  *
ERROR at line 2:
ORA-00904: "D"."DEPTNO": invalid identifier


SQL> ed
Wrote file afiedt.buf

  1  select
  2   (select sum(sum(sal)) s from emp e where e.deptno=d.deptno group by deptno) ss
  3* from dept d
SQL> /

        SS
----------
      8750
     10875
      9400