How to generate serial number in group by sql
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