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It is very helpful to first test your queries by entering the query URL directly into your web browser and verify that the data resultset returned to your browser as a web page is as you expect. Note however that browsers often cache web pages. If you edit your configuration.xml SQL query and reload/refresh the URL in your browser you may NOT get the updated results due to your browser's caching. Avoid this caching issue by always opening a new browser tab to retest and an updated query.