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navigational queries

navigational queries defines queries in terms of classes and values of their (nested) properties

They are not specified in an SQL like language, but directly in filter objects. They are navigational because you may nest properties in navigational paths, something like:

WHERE country.code = 'US'
ODER BY company.name

This will result in SQL with JOINs for country on countryId and for company on companyId. For how to specify such a query in filter objects, see How to create and use filters.