Hi Jan Willem, you should use DATEPART to extract only the date from the DateTime field.
have a look here
example:
SELECT DATEPART(DAY, "FormDate") AS DayNumber
FROM MainModule.myform
If time component is not important I’d suggest that to reset the time value when capturing the data once the form is submitted.
That way when you create the chart information it would be displayed as required. For the existing data in the database you would have to run some kind of script to reset only the time component though.
Hope this help!