Need to reduce table accesses

Question

oracle 9.2.0.8 (if there's a 10G way that would work)
This is a simplified view of a much biiger table I am having to deal with.
create table stg
(ddate date,
num number);
insert into stg
select sysdate, 26 from dual
union all
select sysdate - 1, 38 from dual
union all
select sysdate - 2, 10 from dual
union all
select sysdate - 3, 40 from dual
union all
select sysdate - 4, 50 from dual
union all
select sysdate - 5, 1 from dual
union all
select sysdate - 6, 11 from dual
union all
select sysdate - 7, 50 from dual
union all
select sysdate - 9, 38 from dual
union all
select sysdate - 10, 20 from dual
union all
select sysdate - 11, 11 from dual
union all
select sysdate - 12, 99 from dual
union all
select sysdate - 13, 18 from dual
union all
select sysdate - 14, 27 from dual
union all
select sysdate - 15, 28 from dual
union all
select sysdate - 16, 2 from dual
union all
select sysdate - 17, 99 from dual
union all
select sysdate - 18, 12 from dual
union all
select sysdate - 19, 27 from dual
union all
select sysdate - 20, 28 from dual
select
sum(case when ddate > d.the_date then 1
else 0
end)
,sum(case when ddate < d.the_date then 1
else 0
end)
,the_date
,max(ddate)
from stg, (select min(ddate) as the_date from stg
where num in (10,11,12,13,14,25))d
group by the_date
the query does give me the result set I'm looking for but the explain plan
shows it takes 2 table accesses. My question is how to re-write this so it
takes one access.
I have tried the analytic functions but there does not seem to be a way to
use the where clause in just the analytic function. Also I have tried:
select min(ddate), max(ddate) from stg
where num in (10,11,12,13,14,25)
but the problem with this is the max is the max where num is (10,11,12,13,14,25)not the max of the whole table.
any ideas to get rid of the nested loop would be helpful
thanks

Answer 1

What do you want is not clear for me, but you can try to replace your query :
SCOTT@demo102> select greater,lesser,min_date,max_date
  2  from
  3  (SELECT
  4   SUM(decode(SIGN(ddate -stg_sub."min_date"), 1, 1, 0)) over() AS greater
  5  ,SUM(decode(SIGN(ddate -stg_sub."min_date"), -1, 1, 0)) over() AS lesser
  6  ,stg_sub."min_date" AS min_date
  7  ,stg_sub."max_date" AS max_date
  8  ,rownum AS rnum
  9  FROM
10  (SELECT
11      ddate
12     ,(SELECT MIN(ddate) FROM stg WHERE num IN(10,11,12,13,14,25)) AS "min_date"
13     ,max(ddate) over() AS "max_date"
14   FROM stg)stg_sub)
15  where rnum = 1
16  ;
   GREATER     LESSER MIN_DATE MAX_DATE
        17          2 26/09/06 14/10/06by
SCOTT@demo102> select sum(greater) greater, sum(lesser) lesser, max(min_date) min_date, max(max_date) max_date
  2  from
  3  (SELECT
  4     case when ddate - MIN(case when num IN(10,11,12,13,14,25) then ddate end) over () > 0 then 1 end AS greater,
  5     case when ddate - MIN(case when num IN(10,11,12,13,14,25) then ddate end) over () < 0 then 1 end AS lesser,
  6     MIN(case when num IN(10,11,12,13,14,25) then ddate end) over ()  as min_date,
  7     max(ddate) over() AS max_date
  8   FROM stg)
  9  ;
   GREATER     LESSER MIN_DATE MAX_DATE
        17          2 26/09/06 14/10/06
SCOTT@demo102>
It is a lower cost What did you mean by cost ? Is it cost from explain plan ? Take care, a low cost here doesn't say that your query will run fatser...
Nicolas.