Oracle：从自我联接更新

Question

Given this table:

MODEL   RESULT  DATE    SECTION
AABBCC  10.5    1/1/2001    1
AABBCC  15.6    1/1/2001    2
AABBCC  42.2    1/1/2001    3
AABBCC  35.4    1/1/2001    4
AABBCC  82.1    1/1/2001    5
AABBCC  95.3    1/1/2001    6
AABBCC  76.5    1/1/2001    7

I want to make sure that for each section (for the same date/model), the result is always greater than or equal to any preceding section.

eg If row 7's result is less than row 6's result, I need to set row 7 equal to row 6's result.

Similarly, if row 5's result is less than row 2's result, I would need to set row 5's result to row 2's result.

I am able to find the cases where a higher section has a lower value than a preceding section using a self-join like this:

SELECT 
  t1.MODEL as MODEL,
  t1.DATE as DATE
  t1.RESULT as RESULT_1,
  t1.SECTION as SECTION_1,
  t2.RESULT as RESULT_2,
  t2.SECTION as SECTION_2
FROM table t1
INNER JOIN table t2
ON t1.DATE = t2.DATE AND t1.MODEL = t2.MODEL
WHERE t2.section > t1.section AND
      t2.result < t1.result 

Which produces the following:

MODEL   DATE    SECTION_1   RESULT_1    SECTION_2   RESULT_2
AABBCC  1/1/2001    3   42.2    4   35.4
AABBCC  1/1/2001    6   95.3    7   76.5

I have attempted to MERGE the data like this:

MERGE INTO table new
USING (

SELECT 
  t1.MODEL as MODEL,
  t1.DATE as DATE
  t1.RESULT as RESULT_1,
  t1.SECTION as SECTION_1,
  t2.RESULT as RESULT_2,
  t2.SECTION as SECTION_2
FROM table t1
INNER JOIN table t2
ON t1.DATE = t2.DATE AND t1.MODEL = t2.MODEL
WHERE t2.section > t1.section AND
      t2.result < t1.result 
) old

ON (new.DATE = old.DATE AND new.section > old.section)
WHEN MATCHED THEN
UPDATE
SET new.result = old.result;

but I get the following error:

Error report - SQL Error: ORA-30926: unable to get a stable set of rows in the source tables 30926. 00000 - "unable to get a stable set of rows in the source tables" *Cause: A stable set of rows could not be got because of large dml activity or a non-deterministic where clause. *Action: Remove any non-deterministic where clauses and reissue the dml.

Answer 1

MERGE INTO table new
USING (
SELECT  MODEL,
        DATE,
        RESULT,
        SECTION
FROM (
SELECT 
  t1.MODEL as MODEL,
  t1.DATE as DATE,
  MAX(t1.RESULT) OVER (PARTITION BY t1.MODEL ORDER BY t1.SECTION) as RESULT,
  t1.SECTION as SECTION,
  t1.RESULT as OLD_RESULT
FROM table t1)
WHERE OLD_RESULT != RESULT
) old
ON (new.DATE = old.DATE AND new.section = old.section and new.MODEL = old.MODEL )
WHEN MATCHED THEN
UPDATE
SET new.result = old.result;