On Tue, Sep 2, 2008 at 1:14 PM, Matthew Wilson <matt@xxxxxxxxxx> wrote: > I'm building an app that has a customers table, a locations table, a > products table, and a product_locations table. > > They make a diamond shape. > > The locations table and the products table each have a customer_id > column that links back to the customers table. > > Then the product_locations table table has just two columns: a > location_id column and a product_id column, each linking back to the > appropriate table. > > I want to write a constraint or a trigger or something else that makes > sure that before a (location_id, product_id) tuple is inserted into the > product_locations table, the system verifies that the product links to > the same customer as the location. If the two subordinate tables ALWAYS have to point to the same place, why two tables? Can't a customer have > 1 location? I'm pretty sure IBM has more than one corporate office you could ship things to.
