Uso de la función COALESCE en T-SQL.

Receta_TSQL-3.1_Ej_2.sql

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SELECT c.CustomerID, 
    SalesPersonPhone = spp.PhoneNumber, 
    CustomerPhone = pp.PhoneNumber, 
    PhoneNumber = COALESCE(pp.PhoneNumber, spp.PhoneNumber, 'SIN TELÉFONO')
FROM Sales.Customer c
    LEFT OUTER JOIN Sales.Store s
        ON c.StoreID = s.BusinessEntityID 
    LEFT OUTER JOIN Person.PersonPhone spp 
        ON s.SalesPersonID = spp.BusinessEntityID
    LEFT OUTER JOIN Person.PersonPhone pp 
        ON c.CustomerID = pp.BusinessEntityID
ORDER BY CustomerID;