select  case row_number() over(partition by tbl.tovar order by ...)
          when 1 then tbl.tovar
        end tovar
        ...
  order by tbl.tovar,
           case row_number() over(partition by tbl.tovar order by ...)

SQL> select  case row_number() over(partition by d.dname order by e.ename)
  2            when 1 then d.dname
  3          end dname,
  4          e.job,
  5          e.ename
  6    from  dept d,
  7          emp e
  8    where e.deptno = d.deptno
  9    order by d.dname,
 10             row_number() over(partition by d.dname order by e.ename)
 11  /

DNAME          JOB       ENAME
-------------- --------- ----------
ACCOUNTING     MANAGER   CLARK
               PRESIDENT KING
               CLERK     MILLER
RESEARCH       CLERK     ADAMS
               ANALYST   FORD
               MANAGER   JONES
               ANALYST   SCOTT
               CLERK     SMITH
SALES          SALESMAN  ALLEN
               MANAGER   BLAKE
               CLERK     JAMES
               SALESMAN  MARTIN
               SALESMAN  TURNER
               SALESMAN  WARD

14 rows selected.

SQL> select  case row_number() over(partition by d.dname,e.job,e.ename order by e.ename)
  2            when 1 then d.dname
  3          end dname,
  4          e.job,
  5          e.ename
  6    from  dept d,
  7          emp e
  8    where e.deptno = d.deptno
  9    order by d.dname,
 10             row_number() over(partition by d.dname,e.job,e.ename order by e.ename)
 11  /

DNAME          JOB       ENAME
-------------- --------- ----------
ACCOUNTING     PRESIDENT KING
ACCOUNTING     MANAGER   CLARK
ACCOUNTING     CLERK     MILLER
RESEARCH       CLERK     ADAMS
RESEARCH       ANALYST   SCOTT
RESEARCH       ANALYST   FORD
RESEARCH       CLERK     SMITH
RESEARCH       MANAGER   JONES
SALES          CLERK     JAMES
SALES          MANAGER   BLAKE
SALES          SALESMAN  ALLEN
SALES          SALESMAN  MARTIN
SALES          SALESMAN  TURNER
SALES          SALESMAN  WARD

14 rows selected.

SQL>