Challenging LEFT OUTER JOIN query grouping by MAX - mysql

Question

I have the following two tables:
BillingMatrixDefinition
- id
- amount
BillingMatrix
- definition (FK to table above)
- service_id (FK)
- provider_id (FK)
- amount (Decimal)
I need to get all BillingMatrixDefinitions that have the service_id and provider_id that I specify. Here is the SQL query I currently have:
select def.id, service_id, provider_id,
(case when matrix.amount is not null then matrix.amount else def.amount end) amount
from billing_billingdefinition def
left outer join billing_billingmatrix matrix
on matrix.definition_id=def.id
where (service_id = 25 or service_id is null)
and (provider_id = 24 or provider_id is null)
This gives me the following results:
id service_id provider_id amount
1 25 24 200.00
1 NULL 24 300.00
2 NULL 24 800.00
3 NULL NULL 750.00
5 NULL NULL 450.00
6 NULL NULL 750.00
However, I need to get the billing amount per id, so I can only get ONE item/amount for each id. In which case, I want to get the item where the service_id=24, and if that doesn't exist, then get it where service_id=NULL.
The correct query should give me the following results:
id service_id provider_id amount
1 25 24 200.00
2 NULL 24 800.00
3 NULL NULL 750.00
5 NULL NULL 450.00
6 NULL NULL 750.00
Notice how now there is no duplicate entry for 1, and I use the line item where a service_id has been entered (use that one if it exists, else use NULL). What would be the correct query to do this?

Answer 1

Anothr way:
SELECT
def.id AS id,
COALESCE(matrix.service_id, matrix2.service_id) AS service_id,
COALESCE(matrix.provider_id, matrix2.provider_id) AS provider_id,
COALESCE(matrix.amount, matrix2.amount, def.amount) AS amount
FROM
billing_billingdefinition AS def
LEFT JOIN
billing_billingmatrix AS matrix
ON matrix.definition_id = def.id
AND matrix.service_id = 25
AND matrix.provider_id = 24
LEFT JOIN
billing_billingmatrix AS matrix2
ON matrix2.definition_id = def.id
AND matrix2.service_id IS NULL
AND matrix2.provider_id = 24 ;

Answer 2

Try something along these lines (utilizing a temporary table):
CREATE TEMPORARY TABLE Results
select def.id, service_id, provider_id,
(case when matrix.amount is not null then matrix.amount else def.amount end) amount
from billing_billingdefinition def
left outer join billing_billingmatrix matrix
on matrix.definition_id=def.id
where (service_id = 25 or service_id is null)
and (provider_id = 24 or provider_id is null);
SELECT *
FROM Results r1
WHERE IFNULL(r1.service_id, 0) =
( SELECT MAX(IFNULL(r2.service_id, 0))
FROM Results r2
WHERE r2.id = r1.id
);
SQL Fiddle for the 2nd part only (uses already created Results table)

Answer 3

You need to aggregate the amount using max() (and of course add a group-by clause) so you get the non-null value if one exists:
select
def.id, service_id, provider_id,
max(case when matrix.amount is not null then matrix.amount else def.amount end) amount
from billing_billingdefinition def
left outer join billing_billingmatrix matrix
on matrix.definition_id=def.id
where (service_id = 25 or service_id is null)
and (provider_id = 24 or provider_id is null)
group by def.id, service_id, provider_id

Answer 4

Something like this might work as well.
select def.id, service_id, provider_id, IFNULL(matrix.amount,def.amount) amount
from billing_billingdefinition def
left outer join (select definition_id, max(service_id) as maxsid from billing_billingmatrix matrix group by definition_id) as t1
on def.id = t1.definition_id
left outer join billing_billingmatrix matrix
on matrix.definition_id=def.id and maxsid <=> service_id

Answer 5

I believe PM 771's answer works here as well, but I decided to use a subselect in the OUTER JOIN table, to pre-filter the results before joining.
Here is the final SQL that worked for this:
SELECT *,
(CASE WHEN matrix.amount IS NOT NULL THEN matrix.amount ELSE def.amount END) calculated_amount,
FROM billing_billingdefinition def
LEFT OUTER JOIN
(SELECT t.* FROM (
select * from billing_billingmatrix
where (provider_id=25
or provider_id is null)
and (service_id=24 or service_id is null)
ORDER BY service_id DESC
) t GROUP BY t.definition_id) matrix
ON matrix.definition_id=def.id

Answer 6

Try this:
SELECT BMD.id, BM.service_id, BM.provider_id, IFNULL(BM.amount, BMD.amount) AS amount
FROM BillingMatrixDefinition BMD
LEFT JOIN BillingMatrix BM ON BMD.id = BM.definition_id AND (BM.service_id = 25 OR BM.provider_id = 24)
GROUP BY BMD.id;