How to optimize mapping over several tables - sql

Question

I'm trying to optimize my code. The solution described below works fine, but I'm pretty sure there are better ways to do it. Do you have any recommendations?
I have one table with business contracts and some characteristic attributes:
table_contracts
contract_number attribute_1 attribute_2 attribute_3
123 a e t
456 a f s
789 b g s
And a second table that maps each contract into a specific group. These groups have different priorities (higher number => higher priority). If the attribute column is empty it means that it is not required (=> m3 is the catch all mapping)
table_mappings
map_number priority attribute_1 attribute_2 attribute_3
m1 5 a e t
m2 4 a
m3 3
As a result I need the the contract_number and the corresponding map_number with the highest priority.
This is how I did it, it works but does anyone knows how to optimize that?
with
first_selection as
(
select
table_contracts.contract_number
,table_mappings.priority
,row_number() over(partition by table_contracts.contract_number order by table_mappings.priority desc)
from table_contracts
left join table_mappings
on (table_contracts.attribute_1 = table_mappings.attribute_1 or table_mappings.attribute_1 is null)
and (table_contracts.attribute_2 = table_mappings.attribute_2 or table_mappings.attribute_2 is null)
and (table_contracts.attribute_3 = table_mappings.attribute_3 or table_mappings.attribute_3 is null)
),
second_selection as
(
select
table_contracts.contract_number
,table_mappings.priority
,table_mappings.map_number
from table_contracts
left join table_mappings
on (table_contracts.attribute_1 = table_mappings.attribute_1 or table_mappings.attribute_1 is null)
and (table_contracts.attribute_2 = table_mappings.attribute_2 or table_mappings.attribute_2 is null)
and (table_contracts.attribute_3 = table_mappings.attribute_3 or table_mappings.attribute_3 is null)
)
select
first_selection.contract_number
,second_selection.map_number
from first_selection
join second_selection
on first_selection.contract_number = second_selection.contract_number and first_selection.priority = second_selection.priority
where first_selection.rn = 1
The output of this code would be:
Results
contract_number map_number
123 m1
456 m2
789 m3

Answer 1

I think you only need one of the selections :
with prioritized as(
select c.contract_number, c.attribute_1, c.attribute_2, c.attribute_3, m.map_number
,row_number() over(
partition by c.contract_number
order by m.priority desc
) as rn
from table_contracts c
left join table_mappings m on(
(c.attribute_1 = m.attribute_1 or m.attribute_1 is null)
and (c.attribute_2 = m.attribute_2 or m.attribute_2 is null)
and (c.attribute_3 = m.attribute_3 or m.attribute_3 is null)
)
)
select *
from prioritized
where rn = 1

Answer 2

Try out the below logic using CTE version similar to yours. Hope it helps!
Demo
WITH contracts AS
(SELECT 123 AS contract_number, 'a' AS attribute_1, 'e' AS attribute_2, 't' AS attribute_3 FROM dual
UNION
SELECT 456, 'a', 'f', 's' FROM dual
UNION SELECT 789, 'b', 'g', 's' FROM dual
),
mappings AS
(SELECT 'm1' AS map_number, 5 AS priority, 'a' AS attribute_1, 'e' AS attribute_2, 't' AS attribute_3 FROM dual
UNION
SELECT 'm2', 4, 'a', NULL, NULL FROM dual
UNION
SELECT 'm3', 3, NULL, NULL, NULL FROM dual
),
prioritymap AS
(SELECT contract_number,
map_number,
Rank() over(PARTITION BY contracts.contract_number ORDER BY mappings.priority DESC) AS rank
FROM contracts
JOIN mappings
ON ( contracts.attribute_1 = mappings.attribute_1 OR mappings.attribute_1 IS NULL )
AND ( contracts.attribute_2 = mappings.attribute_2 OR mappings.attribute_2 IS NULL )
AND ( contracts.attribute_3 = mappings.attribute_3 OR mappings.attribute_3 IS NULL )
)
SELECT contract_number, map_number
FROM prioritymap
WHERE prioritymap.rank = 1

Answer 3

You can simply join the tables on the condition given (an attribute is null in the maping table or must match the attribute in the contracts table). Then aggregate per contract number to get the best map_number.
select
c.contract_number,
max(m.map_number) keep (dense_rank last order by m.priority) as map_number
from table_contracts c
join table_mappings m
on (m.attribute_1 is null or m.attribute_1 = c.attribute_1)
and (m.attribute_2 is null or m.attribute_2 = c.attribute_2)
and (m.attribute_3 is null or m.attribute_3 = c.attribute_3)
group by c.contract_number
order by c.contract_number;
Anyway, you are doing this for all contracts and a mapping may match on any combination of attributes, so this will lead to full table scans. The only way I can see to get this quicker is parallel excecution. Maybe the DBMS is set to do this automatically, otherwise you can use a hint:
select /*+parallel(4)*/
...