What he wants is to retrieve all "groups" from a group table together with maximum 10 detailrows from a groupitems table for every group in 1 query.
Just a simple left join, except he wants to limit the number of rows from the second table.
I don't know of any solution coded in 1 SQL (or to lazy to think about it

).
Only a loop through the groups and then fetching max 10 items i can think of.