See ##40867 for the full picture.

* "derived work"
* unset or 0h is the same. It does not count.
* Begin of the deletion setting 0h leads to unset value
* End of the deletion sum from derived work of direct children + self work
* "derived remaining work"
* 0h is actually meaningful here
* sum from derived remaining work of direct children + self remaining work
* it would be nice to make it automatic with a recursive sql statement