Need analytic function suggestion

Question

Hi,
I need advice related to analytic ( I think ) function in Oracle 9.
create table testx ( id number, arr number, fore number, actual number, result_x number, is_first number);
insert into testx values ( 1, null, null, 12, null , 0 );
insert into testx values ( 2, null, null, 14 , null, 0 );
insert into testx values ( 3, 4, 5, 16, 16, 1 );
insert into testx values ( 4, 5, 5, 18, 16, 0 );
insert into testx values ( 5, 5, 5, 20, 16, 0 );
insert into testx values ( 6, 5, 5, 22, 16, 0 );
insert into testx values ( 7, 5, 5, 24, 16, 0 );
insert into testx values ( 8, 5, 5, 25, 16, 0 );
insert into testx values ( 9, 5, 8, 25, 13, 0 );
insert into testx values ( 10, 5, 8, 21, 10, 0 );
insert into testx values ( 11, 5, 8, 19, 7, 0 );
insert into testx values ( 12, 5, 8, 18, 4, 0 );
I need ONE level query ( no subqueries ) which will calculate value stored in RESULT_X column.
Rule for calculation is:
1. when arr and fore columns are available first time then result_x = actual ( row with id = 3)
2. in other case result_x = (previous value of result_x + arr - fore )
3. order of records is stored in id column
I have problem with calculating previous value of result_x since it should be available in next row calculation and dependents on other columns values.
Thanks for help,
Regards,
Piotr

Answer 1

Hi, Piotr,
This produces the results you requested:
SELECT       testx.*
,       SUM ( CASE
              WHEN  is_first = 1
              THEN  result_x
              ELSE  arr - fore
             END
           ) OVER (ORDER BY  id)     AS computed_result_x
FROM      testx
ORDER BY  id
;This relies on the fact that there is only one row where is_first=1, and that all the earlier rows have NULL as arr or fore.
If that's not the case in your real data, then I don't think it's possible in SQL without sub-queries. Why can't you use a sub-query?
The problem is that rows up to the one with is_first=1 have to be treated differently from rows after that point, so ithe CASE expression might need to know if a given row is before or after the one with is_first=1. If you need an analytic function to determine that, then you need a sub-query, becuase analytic functions can not be nested.
You could use MODEL or a recursive WITH clause to get the results you want, but they require sub-querries.