SQL statement -- about index and group by

When I issue an Select statement with group by , is it useful to create a index on the columns in group by function ?

example :

There is a lot of data in Table Table_AA, I use

     SELECT COUNT(*), C_1, C_2, C_3, C_4, C_5
     FROM TABLE_AA
     GROUP BY C_1, C_2, C_3, C_4, C_5

For the performance, do I need to create a index on (C_1, C_2, C_3, C_4, C_5 )
Thank you ! Received on Mon Apr 20 1998 - 00:00:00 CDT