Example: User selects category using the first selectbox on the far left. Then the second selectbox next to it shows brands based on this first selection.
The third selectbox would then show only the products from the selected brand and category.
Then there could of course be other columns for the user to fill and select, in addition to this cascading part which is meant to go through first.
It would be very much like the functionality in Powerful filters add-on, but available for user when adding new rows in editing mode. So, all the selectbox values would be pulled live from the actual database, no manually predefined values anywhere in the cascading part.
Would need to be 2 selectbox levels deep at minimum, preferably up to 4-5 levels possible.
(to make it perfect and extremely useful in different use cases, also consider to include the functionality to allow adding new selectable values as in this suggestion: https://features.wpdatatables.com/252 )