I need to write a sql*plus script that will retrieve all the records that have a date parameter null and not null.
In my sql statement, I have four paramenters: 1) &1 , from po number 2) &2, to po number 3) &3, from promised date 4) &4 , to promised date.  In the data base, the promised date contains a null value.  I need to retrieve all the po with the promise date is null and not null.
****************************
Select poh.segment1 || '?',mtldd.segment1 || '?',
  pl.quantity || '?',  pll.promised_date || '?',
 substr(pll.attribute1,1,1) || '?', substr(pll.attribute1,2,2) || '?', '???0'
 From po_headers_All poh, po_lines_all pl, po_line_locations_all pll,
 mtl_system_items mtldd
 Where  poh.po_header_id = pl.po_header_id
 and mtldd.inventory_item_id = pl.item_id
 and mtldd.organization_id = 303
 And pll.po_header_id = poh.po_header_id
 And pll.po_line_id = pl.po_line_id
 and (poh.segment1 >= nvl('&1', poh.segment1)
 and poh.segment1 <= nvl('&2', poh.segment1))
AND (PLL.PROMISED_date >= to_date('&3','DD-MON-YYYY')
OR (pll.promised_date is null OR (pll.promised_date is  not null)))
AND (PLL.PROMISED_date <= to_date('&4','DD-MON-YYYY')
OR (pll.promised_date is null or (pll.promised_date is  not null)))

If I enter the value for     &1 = (NULL)
                                          &2  (NULL)
                                        &3 = 05 MAR-99
                                       & 4 = 06-MAR-99
   the query retrieves all the po included 01-DEC-98, NOV-23-99, 02-FEB-99 etc..
  it will not retrives the records according to the promise date criteria.

if I change the promised date paramenter to include the (or with only the null value )
then I have a different problem
AND (PLL.PROMISED_date >= to_date('&3','DD-MON-YYYY')
OR (pll.promised_date is null ))
AND (PLL.PROMISED_date <= to_date('&4','DD-MON-YYYY')
or (pll.promised_date is  null))

                     &1 = 10001992
                     &2 =  10002002
                      &3 =   (null)
                    &4 = (null)
the query will retrieve all records base on the search criteria that have a promise date that is null.
But I need to create a query that would retrive all the records that have a date is null and not null.

Please advice!

Thanks
Christine