Join one to many get one row, by priority - sql

Question

I have a contacts table:
ID NAME
--- ----
1 KK
2 JKI
3 HU
And I have a phone table:
ID ContactID Phone Type
--- --------- ----- --------
1 1 569 Business
2 1 896 Mobile
3 1 258 Fax
4 2 369 Mobile
5 3 124 Fax
6 2 496 Fax
I want to get all contacts with at least one phone number. The phone number to be displayed should be Business, if there are no Busniess Type available, then Mobile, if there are no Mobile type available then Fax else null
Sample Result:
ID NAME PHONE
--- ------ ------
1 KK 569 -- Business present
2 JKI 369 -- Business not present but mobile present
3 HU 124 -- only fax present

Answer 1

;WITH [prior](i,t) AS
(
SELECT 1, 'Business'
UNION ALL SELECT 2, 'Mobile'
UNION ALL SELECT 3, 'Fax'
),
x AS
(
SELECT c.ID, c.Name, p.Phone,
rn = ROW_NUMBER() OVER (PARTITION BY c.ID ORDER BY r.i)
FROM dbo.Contacts AS c
LEFT OUTER JOIN dbo.Phone AS p
ON p.ContactID = c.ID
LEFT OUTER JOIN [prior] AS r
ON r.t = p.[Type]
)
SELECT ID, Name, Phone FROM x
WHERE rn = 1;
If you want to eliminate contacts with no phones, just change both instances of LEFT OUTER to INNER.

Answer 2

select c.ID
, c.Name
, coalesce(business.Phone, mobile.Phone, fax.Phone) as Phone
from Contacts c
left join
Phone business
on business.ContactID = c.ID
and business.type = 'Business'
left join
Phone mobile
on mobile.ContactID = c.ID
and mobile.type = 'Mobile'
left join
Phone fax
on fax.ContactID = c.ID
and fax.type = 'Fax'
where coalesce(business.Phone, mobile.Phone, fax.Phone) is not null

Answer 3

Your data model is not great for querying this efficiently, but this may do the trick:
SELECT C.ID, C.Name, COALESCE(
(SELECT TOP 1 P.Phone FROM Phones P WHERE P.ContactID = C.ID AND P.[Type] = 'Business'),
(SELECT TOP 1 P.Phone FROM Phones P WHERE P.ContactID = C.ID AND P.[Type] = 'Mobile'),
(SELECT TOP 1 P.Phone FROM Phones P WHERE P.ContactID = C.ID AND P.[Type] = 'Fax')
) Phone
FROM Contacts C

Answer 4

The most compact solution I can think of is,
; WITH CTE AS (
SELECT
c.ID, c.NAME, p.Phone
, r = ROW_NUMBER()OVER(PARTITION BY c.ID ORDER BY CASE p.[TYPE] WHEN 'Business' THEN 1 WHEN 'Mobile' THEN 2 ELSE 3 END)
FROM Contacts c
LEFT JOIN Phone p ON p.ContactID = c.ID AND p.[TYPE] IN ('Business','Mobile','Fax')
WHERE EXISTS(SELECT 1 FROM Phone WHERE ContactID = c.ID)
)
SELECT ID, NAME, Phone
FROM CTE
WHERE r = 1;
This solution returns,
Contacts with the first matching phone in the specified order
Contact with NULL phone # if a phone # exists but none of the specified types
No result for Contacts having no phone at all