How to get average between rows that are null?

Question

I need to get the average between the 2 positive numbers.
Then update the table with the average for those rows that are NULL between the 2 positive numbers.
The average will come (78+89)/2= 83.5. Round it to 84.
Then it will be:
6-4-13       84
6-5-13        84
6-6-13        84
As for 6-9-13 and 6-10-13, those values will still be NULL.
{code}
create table dummy( tmestmp date
,maxtemp number(4,0));
insert into dummy(tmestmp,maxtemp) values(to_date('20130601','YYYYMMDD'),70);
insert into dummy(tmestmp,maxtemp) values(to_date('20130602','YYYYMMDD'),81);
insert into dummy(tmestmp,maxtemp) values(to_date('20130603','YYYYMMDD'),78);
insert into dummy(tmestmp) values(to_date('20130604','YYYYMMDD'));
insert into dummy(tmestmp) values(to_date('20130605','YYYYMMDD'));
insert into dummy(tmestmp) values(to_date('20130606','YYYYMMDD'));
insert into dummy(tmestmp,maxtemp) values(to_date('20130607','YYYYMMDD'),89);
insert into dummy(tmestmp,maxtemp) values(to_date('20130608','YYYYMMDD'),91);
insert into dummy(tmestmp) values(to_date('20130609','YYYYMMDD'));
insert into dummy(tmestmp) values(to_date('20130610','YYYYMMDD'));
{/code}
I need the output to look like this:
Header 1
Header 2
01-JUN-13
02-JUN-13
03-JUN-13
04-JUN-13
05-JUN-13
06-JUN-13
07-JUN-13
08-JUN-13
09-JUN-13
10-JUN-13
70
81
78
84
84
84
89
91
null
null
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
"CORE 10.2.0.4.0 Production"
TNS for 32-bit Windows: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
Suggestions?
TIA.
Steve42

Answer 1

select  tmestmp,
        nvl(
            maxtemp,
            round(
                   last_value(maxtemp ignore nulls)
                     over(order by tmestmp) +
                   first_value(maxtemp ignore nulls)
                     over(order by tmestmp
                          rows between 1 following and unbounded following
                  ) / 2
           ) maxtemp
  from  dummy
TMESTMP                MAXTEMP
06/01/2013 00:00:00         70
06/02/2013 00:00:00         81
06/03/2013 00:00:00         78
06/04/2013 00:00:00         84
06/05/2013 00:00:00         84
06/06/2013 00:00:00         84
06/07/2013 00:00:00         89
06/08/2013 00:00:00         91
TMESTMP                MAXTEMP
06/09/2013 00:00:00
06/10/2013 00:00:00
10 rows selected.
SQL>
SY.