How do I select nth row from a table

hi ,
I have a table (USR_GROUP_TBL) with  following attributes
  grp_name     char(30)  usr-name     char(15)

In my C program ( with embedded SQL using ecpg)
I need to select  the 'n'th user from the group.
Where n can any value from 1 to Max number of
users in the group.

The following query works well in non-embedded  sql
       select  user_name       from mail_file_dtl       where grp_name = 'grp_1'       order by user_name  limit 1
offset5;
 

Will return the 5th user in the group 'grp_1'.

How can I incorporate this query in  an  embedded sql ??

I tried  the following but ecpg returned error on the last
line.
exec sql       select  mfl_size into :mfl_size       from mail_file_dtl       where mfl_recipient = :mfl_recipient
order by mfl_file_name  limit 1 offset = :nNumber ;
 

Can a variable name be used in the offset option to pass
the value ?

I  encountered a very similar problem when I  tried to use
a cursor  with 'move forward' option.


Thanks
ganesh