Select the highest Id Where serviceId occurs more than once - sql

Question

I have inherited a codebase in Web forms and are having trouble with a SQL query.
SELECT foretag.namn, foretag.epost, foretag.forlangEj, service_fakturering.*
FROM foretag
INNER JOIN service ON foretag.id = service.foretagsid
INNER JOIN service_fakturering ON service.id = service_fakturering.service_id
WHERE service_fakturering.giltighets_datum <= DATEADD(D, 30, GETDATE())
ORDER BY bestallnings_datum DESC, id DESC
In the table service_fakturering there are multiple rows with the same service_id
I need to select the last one, max id, to be used in the INNER JOIN service_fakturering ON service.id = service_fakturering.service_id

Answer 1

Using ROW_NUMBER() function, along with common table expression, it can be done like this:
WITH cte_service_fakturering AS
(
SELECT *, ROW_NUMBER() OVER (PARTITION BY service_id ORDER BY id DESC) RN
FROM service_fakturering
)
SELECT foretag.namn, foretag.epost, foretag.forlangEj, cte.*
FROM foretag
INNER JOIN service ON foretag.id = service.foretagsid
INNER JOIN cte_service_fakturering cte ON service.id = cte.service_id AND cte.RN = 1
WHERE service_fakturering.giltighets_datum <= DATEADD(D, 30, GETDATE())
ORDER BY bestallnings_datum DESC, id DESC

Answer 2

The Sub select will group your service_fakturering rows and get the maxId for you. This is then used to join back into your query and filter for only those rows you are interested in.
SELECT foretag.namn, foretag.epost, foretag.forlangEj, service_fakturering.*
FROM foretag
INNER JOIN service ON foretag.id = service.foretagsid
INNER JOIN service_fakturering ON service.id = service_fakturering.service_id
INNER JOIN (Select service_fakturering.service_id, Max(service_fakturering.id) as Id
FROM service_fakturering
GROUP BY service_fakturering.service_id) x
ON x.service_id = service_fakturering.service_id
AND x.Id = service_fakturering.Id
WHERE service_fakturering.giltighets_datum <= DATEADD(D, 30, GETDATE())
ORDER BY bestallnings_datum DESC, id DESC

Answer 3

Try this...
You could use ROW_NUMBER to denote an order for the set
WITH CTE
AS (
SELECT *
, ROW_NUMBER() OVER (
PARTITION BY service_id ORDER BY ID DESC
) ROWNUM
FROM service_fakturering
)
SELECT foretag.namn
, foretag.epost
, foretag.forlangEj
, service_fakturering.*
FROM foretag
INNER JOIN service
ON foretag.id = service.foretagsid
INNER JOIN service_fakturering
ON service.id = service_fakturering.service_id
AND ROW_NUM = 1
WHERE service_fakturering.giltighets_datum <= DATEADD(D, 30, GETDATE())
ORDER BY bestallnings_datum DESC
, id DESC