Code -- 1. Different Result between "count ep.id" and "count project_id " select ep.id,sub_pl_Lilst.project_id,sub_pl_Lilst.* from eis_projects ep, (select eup.emp_id, eup.project_id,eup.join_date,eup.expected_release_date from eis_user_projects eup, eis_users eu where eup.emp_id = eu.id and eu.active_status ='Y' and eup.user_role_id =2) sub_pl_Lilst --all user project information ,user should be active where ep.id = sub_pl_Lilst.project_id(+) and ep.active_status ='Y'-- all active project PL information -- and ep.id ='' -------------------------------------------------------------------------------------------------- --2. Bai Chi Cuo WU select nvl('','NULL') from dual where1=0; -- no records ,how nvl is working -getting "NO DATA FOUND ERROR " select nvl('','NULL') from dual where1=1; -- 3. ---- no records select* from (select to_date('05/06/2009', 'mm/dd/yyyy') as start_date, to_date('05/16/2009', 'mm/dd/yyyy') as end_date from dual union select to_date('04/06/2009', 'mm/dd/yyyy') as start_date, to_date('04/16/2009', 'mm/dd/yyyy') as end_date from dual union select to_date('03/06/2009', 'mm/dd/yyyy') as start_date, to_date('03/16/2009', 'mm/dd/yyyy') as end_date from dual) where1=0; -- 2 records select to_date('05/06/2009', 'mm/dd/yyyy') as start_date, to_date('05/16/2009', 'mm/dd/yyyy') as end_date from dual union select to_date('04/06/2009', 'mm/dd/yyyy') as start_date, to_date('04/16/2009', 'mm/dd/yyyy') as end_date from dual union select to_date('03/06/2009', 'mm/dd/yyyy') as start_date, to_date('03/16/2009', 'mm/dd/yyyy') as end_date from dual where1=0;--!!!