You can create an Adobe CQ web application that performs database operations on a relational database. For example, you can create an Adobe CQ web application that retrieves data from MySQL and displays the data in a JSP. The following illustration shows data being retrieved from a relational database and displayed in a JSP.
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If you are interested in learning how to persist Adobe CQ data into MySQL, click here: http://scottsdigitalcommunity.blogspot.ca/2013/01/persisting-adobe-cq-data-in-relational.html.