Below is a relational schema for the Northwind database (a sample company suppli

Question

Below is a relational schema for the Northwind database (a sample company supplied with Microsoft Access).

Notes:
Primary keys are underlined.
EMPLOYEES.ReportsTo is the employee number of the employees' supervisor.
ORDERS has the header for each order, whereas ORDER_DETAILS has the line items for the products ordered.
PRODUCTS.UnitsOnOrder refers to the product being ordered from a supplier for restocking, and not to a customer having placed an order for it.
ORDERS.ShipVia is the shipper for this order

Identify all foreign keys in the above schema - state any assumptions you make. Note that the foreign key name may not match the spelling of the corresponding primary key.

CUSTOMERS CustomerID, CompanyName, ContactName, ContactTitle, Address, City, Region, PostalCode, Country, Phone, Fax EMPLOYEES EmployeeID, LastName, FirstName, TitleOfCourtesy, BirthDate, HireDate, Address, City, Region, PostalCode, Country, HomePhone, Extension, ReportsTo PRODUCTS ProductID, ProductName, Supplier, Category, QuantityPerUnit, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued CATEGORIES CategoryID, CategoryName, Description SHIPPERS ShipperID, CompanyName, Phone SUPPLIERS SupplierID, CompanyName, ContactName, ContactTitle, Address, City, Region, PostalCode, Country, Phone, Fax, HomePage ORDERS OrderID, Customer, Employee, OrderDate, RequiredDate, ShippedDate, ShipVia, Freight, ShipName, ShipAddress, ShipCity, ShipRegion, ShipPostalCode, ShipCountry ORDER_DETAILS Order, Product, UnitPrice, Quantity, Discount

Explanation / Answer

A foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table, thus the following tables only has foreign keys, which are listed below

PRODUCTS : Category (links to CATEGORIES.CategoryID)

ORDERS : Customer (links to CUSTOMERS.CustomerID), Employee (links to EMPLOYEES.EmployeeID), ShipVia (links to SHIPPERS.ShipperID)

ORDER_DETAILS : Order (links to ORDERS.OrderID), Product (links to PRODUCTS.ProductID)

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