forming a query based on condition for displaying records in grid on demand

i have a function or binding grid where i pass the flag for query to be displayed for page load i have below query if (flag=="pageload) { sql= "select  ";                     sql= sql *  "  from (select top  50   *  "  from ";                     sql= sql+ "(select top  50  *   from EMPLOYEE  order by NAME )";                     sql= sql+ " as T1 order by T1.NAME  DESC) as T2 order by NAME  ASC  "; } else if flag=="filteration select * from EMPLOYEE in the above query i get 50 records per page & the next prev navigation works fine bbut when i filter out the records  i cant use the above query to get the filtered records as  ii need to filter from the whole recordset say i have total 1000 records after filteering i get 500 records after filteration i am not able to navigate across the records correctly