Question

I have a simple table schema:

Person: ID, Name
PhoneNumber: ID, Type, Number                    #Type can be 'home' or 'mobile'.
PersonPhoneNumber: ID, Person_ID, PhoneNumber_ID #A join table that connects the
                                                 #person to a phone number.

As data I have:

Person: 1, "Ed"
PhoneNumber: 1, "home", 1111
PhoneNumber: 2, "mobile", 2222
PersonPhoneNumber: 1, 1 /*(Person_ID)*/, 1 /*(PhoneNumber_ID*/
PersonPhoneNumber: 2, 1 /*(Person_ID)*/, 2 /*(PhoneNumber_ID*/

I want to write a view that returns:

Name    |Home    |Mobile
-----------------------------
"Ed"     1111     2222
"Joe"    3333     4444
... etc

Any tips on how I approach this?

Note: These tables are a snippet from a larger schema which explains why its a many to many and not more simplistic.

Answer 1

You could do this in a more complicated way if you have multiple numbers or might have more than home/mobile, but for now, if you only have two numbers, then this will work:

SELECT Name, HomeNumber.Number AS Home, MobileNumber.Number AS Mobile
FROM Person
    LEFT JOIN PersonPhoneNumber HomeMap
        ON Person.ID = HomeMap.Person_ID
    LEFT JOIN PhoneNumber HomeNumber
        ON HomeMap.PhoneNumber_ID = HomeNumber.ID AND HomeNumber.Type = 'home'
    LEFT JOIN PersonPhoneNumber MobileMap
        ON Person.ID = MobileMap.Person_ID
    LEFT JOIN PhoneNumber MobileNumber
        ON MobileMap.PhoneNumber_ID = MobileNumber.ID AND MobileNumber.Type = 'mobile'

BTW, if you dont want people with any numbers, then you can make the PersonPhoneNumber mapping a JOIN instead of a LEFT JOIN