In a scenario where you are working with a large dataset in Azure Databricks that contains 'product_name' and 'category' columns, your task is to ensure data integrity by validating that each 'product_name' is associated with only one unique 'category' value. Considering the need for efficiency and accuracy in a production environment, which of the following Spark SQL queries would you use to identify any 'product_name' that violates this uniqueness constraint by being associated with more than one 'category'? Choose the best option.