R – How to connect to a Oracle Database from Web Services Published on IIS

To find the sessions, as a DBA use

select sid,serial# from v$session where username = '<your_schema>'

If you want to be sure only to get the sessions that use SQL Developer, you can add and program = 'SQL Developer'. If you only want to kill sessions belonging to a specific developer, you can add a restriction on os_user

Then kill them with

alter system kill session '<sid>,<serial#>'

(e.g. alter system kill session '39,1232')

A query that produces ready-built kill-statements could be

select 'alter system kill session ''' || sid || ',' || serial# || ''';' from v$session where username = '<your_schema>'

This will return one kill statement per session for that user - something like:

alter system kill session '375,64855';

alter system kill session '346,53146';

You can use a subquery for this like

select *
from  
( select * 
  from emp 
  order by sal desc ) 
where ROWNUM <= 5;

Have also a look at the topic On ROWNUM and limiting results at Oracle/AskTom for more information.

Update: To limit the result with both lower and upper bounds things get a bit more bloated with

select * from 
( select a.*, ROWNUM rnum from 
  ( <your_query_goes_here, with order by> ) a 
  where ROWNUM <= :MAX_ROW_TO_FETCH )
where rnum  >= :MIN_ROW_TO_FETCH;

(Copied from specified AskTom-article)

Update 2: Starting with Oracle 12c (12.1) there is a syntax available to limit rows or start at offsets.

SELECT * 
FROM   sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;

See this answer for more examples. Thanks to Krumia for the hint.