How to generate serial number in group by sql

Question

I need the query output with record serial number by a group,
Sr No by dept Dept Id Emp Name
========= ===== =======
1 10 aaaaa
1 11 abndddd
2 11 sdfffffff
3 11 s sdfe
4 11 ggg
1 12 dDEWQ
1 13 xccc
2 13 DSAFG
How to generate the first column in the above output using sql?
Thanks in advance
Shrinivas

Answer 1

use the analytic function ROW_NUMBER
here is a small example
SQL> select row_number() over(partition by deptno order by empno) rno, deptno, empno
  2    from emp
  3  /
       RNO     DEPTNO      EMPNO
         1         10       7782
         2         10       7839
         3         10       7934
         1         20       7566
         2         20       7788
         3         20       7876
         4         20       7902
         1         30       7499
         2         30       7521
         3         30       7654
         4         30       7698
       RNO     DEPTNO      EMPNO
         5         30       7844
         6         30       7900
13 rows selected.