SQL Server : replace UDF with a joined view - sql-server

Question

I'd would like to ask your help with a gordian knot in my head with regards to SQL Server. I'm trying to replace an UDF with a joined view, but I'm struggling to get the view to return what I need. A bit of clever ordering or so may well do the trick, I'm stuck.
Unfortunately I can't sign up to SQL fiddle at the moment so I have to present the test data here:
CREATE TABLE #Contacts
(
ID INT NOT NULL IDENTITY,
Firstname VARCHAR(50) NULL,
Lastname VARCHAR(50) NULL
)
GO
CREATE TABLE #Cars (ID INT NOT NULL IDENTITY, CarModel VARCHAR(50) NULL)
GO
CREATE TABLE #Ownership
(
Contacts_ID INT NOT NULL,
cars_id INT NOT NULL,
ownership_type TINYINT NOT NULL,
DisplayName VARCHAR(50) NULL
)
GO
CREATE TABLE #Races(ID INT NOT NULL IDENTITY, RaceName VARCHAR(50) NOT NULL)
GO
CREATE TABLE #RaceEntries
(
ID INT NOT NULL IDENTITY,
Races_ID INT NOT NULL,
Contacts_ID INT NOT NULL,
cars_id INT NOT NULL
)
INSERT [#Contacts] ([Firstname], [Lastname])
SELECT
'Justin', 'Case' UNION ALL SELECT
'Gladys', 'Friday' UNION ALL SELECT
'Mandy', 'Lifeboats'
GO
INSERT [#Cars] ([CarModel])
VALUES ('Great Car')
GO
INSERT [#Races] ([RaceName])
VALUES ('A Car Race')
INSERT [#Ownership] ([Contacts_ID], [cars_id], [ownership_type], [DisplayName]) SELECT
1, 1, 0, NULL UNION ALL SELECT
2, 1, 1, NULL UNION ALL SELECT
3, 1, 1, 'Mandy Lifeboats Racing Team'
INSERT [#RaceEntries] ([Races_ID], [Contacts_ID], [cars_id]) SELECT
1, 1, 1 UNION ALL SELECT
1, 3, 1 UNION ALL SELECT
1, 2, 1
What I'd like:
SELECT
[cars_id], mvo.Ownername
FROM
[#RaceEntries] -- join a view that returns the ownername
LEFT OUTER JOIN
#myViewOwnername AS mvo ON mvo.Contacts_ID = [#RaceEntries].[Contacts_ID] AND mvo.Cars_ID = [#RaceEntries].[cars_id]
The issue here is that every car only has one owner (type 0 in ownership). It can have other contacts as representatives.
Usually on lists for #RaceEntries, the owner's name is displayed, unless the representative has an agreed "an override" (so that his or a company name is displayed).
In the above example, for Justin Case's entry it's straight-forward. He is the owner (type 0), end of story.
When Gladys Friday enters (she doesn't have an override "DisplayName") the system should again return Justin Case's name as the owner.
In the last example, Mandy Lifeboats has a DisplayName and therefore that should be returned.
Ideally, I would end up with a view or similar that does the heavy lifting, so that I can join it to x000 records from #RaceEntries (joined on car and contact ID) to get the correct owner name back.
I hope I've simplified the example as much as possible, the real thing is a bit more complex... Please let me know if I should prepare anything else to make helping a bit easier. Many thanks!

Answer 1

I think this might be what you are looking for:
select [#Ownership].Contacts_ID,
[#Ownership].Cars_ID,
coalesce([DisplayName], CarOwners.ContactName) Ownername
into #myViewOwnername
from [#Ownership]
join
(
select [cars_id], Contacts_ID, [#Contacts].Firstname + ' ' + [#Contacts].Lastname ContactName
from [#Ownership]
join [#Contacts]
on [#Ownership].Contacts_ID = [#Contacts].ID
where ownership_type = 0
) CarOwners
on [#Ownership].cars_id = CarOwners.cars_id
A car has one direct owner (type 0), so the sub-query will get you all the owner names of each car. Then you just join that to your ownership table on the cars_id fields. If there is a display name in the ownership table you display that, otherwise you show the car owner's name.