@munmun,
Do you have a sample project with datetime picker attached to it
Please take a look at this JSFiddle.
kindly check for this if possible why only double parameters can plot the graph from database and not string / date type data.
CanvasJS supports numeric and date-time as x-values and when it comes to date-time, it should be JavaScript date object or timestamp. If you like to use string, you can use labels. To pass Java date to JavaScript, you would need to convert Java date to timestamp in milliseconds and pass it to JavaScript. Please refer this stackoverflow thread for more information.
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Indranil Deo
Team CanvasJS