Joins between sharepoint list

Referencing and Linking: Using Secondary Lists to Maintain Relationships in SharePoint Server 2007
Learn how to extend a custom Relationship field in Microsoft Office SharePoint Server 2007 to enable users to select a relationship type and store information in a secondary table. Click here to read more
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In many scenarios, we SharePoint developers want to take two different lists and join them and present a single set of data. For instance, one list contains customer information and the other list contains products with serial numbers and customer-related specific details like connection information and versions. There is a lookup field in the product list that selects the customer the product belongs to. So far so good :) Click here to read more