Searching - All projects with no Next Action

[Quantum7]

NextAction is indeed an attribute I created (GTD related). Yes/No checkbox in case you want to reproduce .

Hmmmm, this is a slightly simplified version of my problem:
I want the search to return all the projects that have at least one task as child that hasn't got a "Completed" flag yet.

The basic problem I'm having here seems to be:
- I'm already searching for projects and I don't have a way in which to specify a condition which applies to it's childs.

In more technical terms: I'd probably need to do a query within a query, which doesn't seem possible with the current advanced search.

Note:
I did succeed in making a search which returns all the projects that have no children as there's a specific "HasChildren" derived attribute available.