Turn many to many relationship into single row - sql-server

Question

I have the following tables
Users
Id
FirstName
LastName
Sample Data
1,'Peter','Smith'
2,'John','Como'
Phones
Id
UserId
PhoneTypeId
Phone
ContactName
Sample data
1,1,4,'555-555-5551','Peter'
2,1,4,'555-555-5552','Paul'
3,1,4,'555-555-5553','Nancy'
4,1,4,'555-555-5554','Hellen'
PhoneTypes
Id
Type
with sample data
1 Home
2 Work
3 Cell
4 Emergency
I have to create following result
UserId, UserFirstName, UserLastName, FirstEmergencyContactName, FirstEmergencyContactPhone, SecondEmergencyContactName, SecondEmergencyContactPhone, ThirdEmergencyContactName, ThirdEmergencyContactPhone, FourthEmergencyContactName, FourthEmergencyContactPhone, FifthEmergencyContactName, FifthEmergencyContactPhone
How can I create a single row for every user with emergency contacts? Some of the users might have one emergency contact and others might have many, but I need only five of them.

Answer 1

This is called table pivoting. Since you want no more than 5 results, you can use conditional aggregation with row_number:
select id, firstname, lastname,
max(case when rn = 1 then contactname end) emergency_contact1,
max(case when rn = 1 then phone end) emergency_phone1,
max(case when rn = 2 then contactname end) emergency_contact2,
max(case when rn = 2 then phone end) emergency_phone2,
...
from (
select u.id, u.firstname, u.lastname, p.phone, p.contactname,
row_number() over (partition by u.id order by p.phonetypeid) rn
from users u
join phones p on u.id = p.userid
) t
group by id, firstname, lastname

Answer 2

Also you can use pivoting, without dynamic SQL and hard-coding, because you need only 5 contacts/phones. Example below:
;WITH cte AS (
SELECT p.UserId,
FirstName,
LastName,
CAST(ContactName as nvarchar(100)) as ContactName,
CAST(Phone as nvarchar(100)) as ContactPhone,
CAST(ROW_NUMBER() OVER (PARTITION BY p.UserId ORDER BY pt.Id) as nvarchar(100)) as RN
FROM Users u
INNER JOIN Phones p
ON p.UserId = u.Id
INNER JOIN PhoneTypes pt
ON pt.Id = p.PhoneTypeId
WHERE pt.Id = 4
)
SELECT *
FROM (
SELECT UserId,
FirstName,
LastName,
[Columns]+RN as [Columns],
[Values]
FROM cte
UNPIVOT (
[Values] FOR [Columns] IN (ContactName, ContactPhone)
) as unp
) as t
PIVOT (
MAX([Values]) FOR [Columns] IN (ContactName1,ContactPhone1,ContactName2,ContactPhone2,ContactName3,ContactPhone3,
ContactName4,ContactPhone4,ContactName5,ContactPhone5)
) as pvt
Output:
UserId FirstName LastName ContactName1 ContactPhone1 ContactName2 ContactPhone2 ContactName3 ContactPhone3 ContactName4 ContactPhone4 ContactName5 ContactPhone5
1 Peter Smith Peter 555-555-5551 Paul 555-555-5552 Nancy 555-555-5553 Hellen 555-555-5554 NULL NULL
2 John Cono Harry 555-555-5555 William 555-555-5556 John 555-555-5557 NULL NULL NULL NULL
I add some more contacts.