TomTurtle

Great! Thank you very much for your help! :-)

Unfortunately I have identified a weak point in this solution... this option hides ALL unused dropdown options, even from the first dropdown. For example when I have a dropdown "Databases"...

yes, this does work. but if there would be a column-specific possibility one would only have to select another database instead of clicking 2 times (1. clear, 2. select)