Rank records in db2 sql

Question

I have 2 table like below,

product1    item1   rank1
1234    XXXX    1
1234    YYYY    2
5678    GGGG    3
5678    HHHH    4

product2    item2   score   rank2
 1234       XXXX    90        1
 1234       ZZZZ    80        2
 1234       YYYY    70        3
 1234       CCCC    60        4
 5678       HHHH    80        1
 5678       GGGG    60        2
 5678       DHDH    50        3
 9800       AAAA    100       1
 4352       BBBB    45        1

I need the output of table 2 to be changed like below,

product2    item2   score   rank2
1234         XXXX   90        1
1234         YYYY   70        2
1234         ZZZZ   80        3
1234         CCCC   60        4
5678         GGGG   60        1
5678         HHHH   80        2
5678         DHDH   50        3
9800         AAAA   100       1
4352         BBBB   45        1

The below SQL provides the below output,

SELECT PRODUCT2,LINE2,SCORE,ROWNUMBER() 
OVER (Partition by PRODUCT1 order by A.RANK1 ) RANK
FROM TABLE1 A, TABLE2 B WHERE A.ITEM1= B.ITEM2 AND
A.PRODUCT1 = B.PRODUCT2
UNION ALL
SELECT PRODUCT2,LINE2,SCORE,
ROWNUMBER() OVER (Partition by PRODUCT2 ORDER BY SCORE DESC) RANK
FROM TABLE2 C
WHERE NOT EXISTS (
SELECT * FROM TABLE1 A WHERE A.PRODUCT1 = C.PRODUCT2 
AND A.ITEM1= C.ITEM2)

product2    item2   score   rank2
1234        XXXX     90       1
1234        YYYY     70       2
1234        ZZZZ     80       1
1234        CCCC     60       2
5678        GGGG     60       1
5678        HHHH     80       2
5678        DHDH     50       1 
9800        AAAA     100      1
4352        BBBB     45       1

The lines which are not available in table1 are not getting the increment rank after the comparison of table2 but instead of that they are getting the new rank starting it as 1. can someone please look into this and advise me on how to achieve the expected results in db2 ?

Input :

Table 1:

Product1 item1 rank1
12345    Xxxx    1
12345    yyyyy   2
12345    Cccc    3
67890    Aaaa    4

Table2:

Product2. Item2   score rank2
12345       Bbbb    90      1
12345       yyyyy   80      2
12345       Xxxx    70      3
12345       Cccc    60      4
67890       Aaaa    95      1
67890       Bbbb    85      2
56789       Ghsg    67      1
45377       Hhhh    70       1

Expected output :

Product2.   Item2.   Score.   Rank
12345        Xxxx    70          1
12345        yyyyy   80          2
12345        Cccc    60          3
12345        Bbbb    90          4
67890        Aaaa    95          1
67890        Bbbb    85          2
56789        Ghsq    67          1
45377        Hhhh    70          1

Answer 1

SELECT PRODUCT2, LINE2, SCORE,
   CASE WHEN A_ITEM1 IS NULL THEN RANK2 ELSE RANK END AS RANK
FROM (
  SELECT PRODUCT2, LINE2, SCORE,
    A.ITEM1 A_ITEM1,
    ROWNUMBER() OVER (Partition by PRODUCT1 order by A.RANK1 AS  RANK,
    ROWNUMBER() OVER (Partition by PRODUCT2 order by B.SCORE AS  RANK2
  FROM TABLE1 B
  LEFT JOIN TABLE1 A ON A.ITEM1 = B.ITEM2 AND A.PRODUCT1 = B.PRODUCT2
) Z

Answer 2

try this :

with t1 as (
select f1.*, rownumber() over(partition by f1.Product1 order by f1.rank1) rank
from table1 f1
),
t2 as (
select f1.*, rownumber() over(partition by f1.Product2 order by f1.score desc) rank
from table2 f1
)
select t2.Product2, ifnull(t1.item2, t2.item2) item2, t2.score, t2.rank as rank 
from t2 left outer join t1 on t1.Product1=t2.Product2 and t1.rank=t2.rank