SQL & PL/SQL

  friends i need to update my employee master table which having some 50000+ record so i want to update it in 1000 records one time 
  because it is having trigger which calling some function and procedure ..

  i tried with this 
  
--update prm_m_employee 
--set PMEP_BASIC_FLAG = 'Y'

  select rownum , pmep_emp_id , pmep_psno 
from prm_m_employee
where exists ( select distinct 'x' 
               from prm_m_chart_17 
               where  PMC17_F17_CODE  = pmep_emp_id 
               and PMC17_HOP_CODE = 5 )
and rownum between 1 and  1000

but  for next thousnd it is not returning 

 please give any suggestion