How do I select only the green summary lines from the database, after I have grouped up
Simply choose your desired Outline level from the Field Menu’s Analyze submenus.
You could also, in the Find/select dialog, choose from the popup “Formula is true”. Then, for the formula, type in info("summary")>0. Understanding the latter is the door to making more complex summary selection formulas.
For most applications this is probably the correct answer.
Please keep in mind that selecting summaries this way is not quite the same thing as collapsing summaries with the Outline menu. You can select summary records this way, but then the only way to make the original data visible again would be to use another selection – you won’t be able to do so with the Outline menu. None of this is a problem - but it could be confusing if you aren’t aware of the difference.