Question

I have a Contacts table and a Businesses table, they are joined via a Contacts_vs_Businesses table (it’s a many-to-many relationship).

I want to query the two tables; if a contact is related to two businesses, I want to return:

• A row with all contact details and all details of Business A;
• A row with all contact details and all details of Business B
• A row with all contact details and NO business details at all (as if I’d just done a basic SELECT on the first table)

Contacts Table

ID Contact_Name Contact_Phone
1  Jez Clark    01234 567 890
2  Someone Else 01254 648 654

Businesses Table

ID Business_Name   Business_Address
1  A Company       24, A Street, A Town
2  Another Company 43, Another Street, Another Town

Contacts_vs_Businesses

Contact_ID Business_ID
1          1
1          2
2          2

I want to return:

Contact_Name Contact_Phone Business_Name   Business_Address
Jez Clark    01234 567 890 A Company       24, A Street, A Town
Jez Clark    01234 567 890 Another Company 43, Another Street, Another Town
Jez Clark    01234 567 890 NULL            NULL

I’m on SQL Server 2008 R2.

How would I go about this (I’m guessing it’s something REALLY easy…)? I’ve tried the various permutations of OUTER and INNER and LEFT/RIGHT joins, but none seem to give me that last line of results.

Thanks

Answer 1

If I’m understanding your question correctly, for any contact that is associated with 2 businesses, you want to show that contact with each business, followed by a NULL business, resulting in 3 records?

Try something like this using GROUP BY to get counts and UNION to return the NULL record:

SELECT C.Contact_Name, C.Contact_Phone, B.Business_Name, B.BusinessAddress
FROM Contacts C
  INNER JOIN Contacts_vs_Businesses CB ON C.Id = CB.Contact_ID
  INNER JOIN Businesses B ON CB.Business_Id = B.Id
  INNER JOIN (SELECT Contact_ID, COUNT(*) cnt FROM Contacts_vs_Businesses GROUP BY Contact_ID) CB2 ON C.Contact_ID = CB2.Contact_Id      
WHERE CB2.cnt = 2
UNION
SELECT C.Contact_Name, C.Contact_Phone, NULL, NULL
FROM Contacts
   INNER JOIN Contacts_vs_Businesses CB ON C.Contact_ID = CB.Contact_Id      
GROUP BY C.Contact_Name, C.Contact_Phone
HAVING Count(*) = 2

Good luck.