SQL Query to get specific child records - sql

Question

I have a requirement to get child table records based on parent table search criteria but they need to be distinct and output should be like below:
Table A, have three rows. Row one is for generic rules, Row 2 is for specific Category and Row 3 is for Specific Branch, Category and Sub-Category.
Now, my output should consists of the rules which are specific to generic.
Below are the rules for the output:
Input to the query will be Branch, Category and Sub-Category
Each record-set in Table-A is comprised of 03 rows
Row 1 has Branch but Category and Sub-Category as Null
Row 2 has Branch and Category Sub-Category as Null
Row 3 has Branch, Category and Sub-Category.
Each Row in a record-set of Table-A has child records in Table-B
Record with Branch only (Row 1), have generic records and these records can also be child records of Row 2 and Row 3
Record with Branch and Category Sub-Category as Null (Row 2) has child records in Table-B and they are overriding child records of Row 1
Record with Branch, Category and Sub-Category (Row 3) has child records in Table-B and they are overriding child records of Row 1 and Row 2.
All child records of Row 1,2 & 3 will be part of the output but if a child is present in Row 3 then despite if it is present in other Rows output will consists of child record of Row 3
If a child record is present in Row 1 & 2 but not in 3 then output
will have child record of Row 2
if a child record is present in Row 1 but not in Row 2 & 3 then it
will be part of output.
Now,
In the sample output, 'Pay' is present in Row 1,2 and 3 but in the
output we are considering child record of Row 3 as it overrides both Record 1 & 2
'Discount' is present in Record 1 & 3 but output includes child of Row 3
'Items' is not part of Row 1 and Row 2 childs but as it is present in Row 3 so it will be part of output
'Paris' is only part of Row 2 but as it is not overriden by Row 2 so
it is part of output as it is
I have tried following query but it is not giving the required output:
SELECT DISTINCT RULE,
value
FROM siebel.b rxm
WHERE par_row_id IN (SELECT row_id
FROM siebel.a
WHERE ( branch = 'Civil'
AND category = 'C.M.> (Civil)'
AND sub_category IS NULL )
OR ( branch = 'Civil'
AND category = 'C.M. (Civil)'
AND sub_category = 'Pauper' )
OR ( branch = 'Civil'
AND category IS NULL
AND sub_category IS NULL ))
I am using Oracle as RDBMS.
Schema statements:
Create Table A (ROW_ID int, BRANCH varchar(50), CATEGORY varchar(50), SUB_CATEGORY varchar(50))
Create Table B (PAR_ROW_ID int, RULE varchar(50), Value varchar(50))
INSERT INTO A (ROW_ID, BRANCH)
VALUES (1,'Civil')
INSERT INTO A (ROW_ID, BRANCH, CATEGORY)
VALUES (2,'Civil','C.M. (Civil)')
INSERT INTO A (ROW_ID, BRANCH, CATEGORY, SUB_CATEGORY)
VALUES (3,'Civil','C.M. (Civil)','Pauper')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (1,'Pay','10')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (1','Days','25')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (1,'Discount','20')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (2,'Pairs','5')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (2,'Pay','30')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (3,'Pay','15')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (3,'Discount','20')
INSERT INTO B (PAR_ROW_ID, RULE, VALUE)
VALUES (3,'items','30')

Answer 1

SELECT MAX( par_row_id ) AS par_row_id,
rule,
MAX( value ) KEEP ( DENSE_RANK LAST OVER ORDER BY par_row_id ) AS value
FROM table_b
GROUP BY rule
Or:
SELECT par_row_id,
rule,
value
FROM (
SELECT b.*,
ROW_NUMBER() OVER ( PARTITION BY rule ORDER BY par_row_id DESC ) AS rn
FROM table_b b
)
WHERE rn = 1;