select distinct
    emp.First_Name,emp.Last_Name,emp.Middle_Name,
    comp.employee_id,comp.request_dt,comp.numofdays,
    comp.reason,comp.request_by,comp.approve_dt,
    tech.First_Name+'  ' +tech.Last_Name+' '+isNull(tech.Middle_Name,'') as REQUESTEDBY,
    comp.approve_status,comp.approve_desc,
     case when (comp.approve_by) is null then '' else ( select first_name+' '+last_name from employee_tbl where user_id=comp.approve_by) end  as APPROVEBY 
from 
    employee_tbl emp,tl_compoff_tbl comp,TL_activity_tbl tla
    ,employee_tbl tech
 
where emp.employee_id = comp.employee_id 
and comp.employee_id = tla.employee_id
and emp.employee_id = tla.employee_id
 and comp.request_by = 'AST/016'         
 and emp.employee_status = 'A'  
 and (comp.approve_status='O' or comp.approve_status='D') 
 and tla.status='A'
 and getdate() between tla.start_date and tla.end_date
and tech.User_Id = comp.request_by
order by comp.approve_status--emp.First_Name