This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
It all boils down to my ignorance concerning SQL, your example does the trick.
It's almost a perfect solution, there's just a single nag about it: Subqueries can only return a single column, so I cannot use yor SELECT ... GROUP BY-query as a subquery. As I see it, the SELECT ... GROUP BY-query must involve columns name and number to produce the desired result or am I overlooking something?
Oh, and another thing: Say your Subquery idea worked. Given the dataset in my previous post, it would return a list containing the values [3, 1, 2] and hence the objects with id 3, 4, 6 would be returned, right? What if the 6th row of the dataset was deleted, then the subquery would return a list containing the values [3, 1, 1], right? If this is correct, how does the outer SELECT know which objects to return, as the values aren't unique? Just a thought...
But thank you very much for your input, it most certainly solved my problem!