Sample Query In TOAD using a 'date' variable:
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declare dt date;
pp varchar(100);
begin
dt:=TO_DATE('2008/04/25', 'yyyy/mm/dd');
select CEIL((SYSDATE - 180) - Decode(dt,null,(SYSDATE - 180),dt)) into pp from dual;
dbms_output.PUT_LINE(pp);
end;