You don't. MySQL is backend, charts.js is frontend.
I don't know it as I'm not a frontend developer, but usually these type of solutions either require you to generate and include the data for the chart in the HTML/Javascript output that the View generates, or you use an Ajax call to have the chart fetch the data using a callback. In which case you need a REST controller that provides the data for the chart in a json structure.
On the Fuel side, you need to create a Controller that extends Controller_Rest, which contains an action method that does the DB query to retrieve your data, and returns it as an array. The controller will convert it to a json response for you. What it needs to return depends obviously on what chart.js expects.
Once done, have the ajax call call your controller.
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