Question

Does anyone have a process or approach to use for determining how to resove a many-to-many relationship in a relational database? Here is my scenario. I have a group of contacts and a group of phone numbers. Each contact can be associated with multiple phone numbers and each phone number can be associated with multiple contacts.

A simple example of this situation would be an office with two employess (e1 & e2), one main voice line (v1), one private voice line (v2). e1 is the CEO so they have thier own private voice line, v1, but they can also be reached by calling the main line, v2, and asking for the CEO. e2 is just an employee and can only be reached by calling v2.

So, e1 should be related to v1 & v2. e2 should be related to v2. Conversly, v1 should be related to e1 and v2 should be related to e1 & e2.

The goal here is to ge able to run queries like ‘what numbers can e1 be reached at’ and ‘what employees can be reached at v2’, etc.. I know the answer will involve an intermediate table or tables but I just can’t seem to nail down the exact architecture.

Answer 1

Employees:

eID, eName 1, e1 2, e2 

PhoneNumbers:

pID, pNumber 1, v1 2, v2 

EmployeePhones:

eID, pID 1, 1 1, 2 2, 2 

then you inner join. if you need to find out what number(s) e1 can be reached at (t-sql):

SELECT E.eName, P.pNumber  FROM   dbo.Employees E  INNER JOIN dbo.EmployeePhones EP ON E.eID = EP.eID  INNER JOIN dbo.PhoneNumbers P ON EP.pID = P.eID  WHERE E.eName = 'e1' 

I believe this should work (testing it right now…)

EDIT: Took me a few minutes to type up, sorry for duplication…