Most DBs don't (and won't ever) support that because the results become undefined. You could get different values out for the same query in different versions of the DB (due to query planner changes) or even within the same version and the same database over time (as the relative sizes of your tables change so the planner choses a different route, or index options are changed, so the planner is forced to go with a different route or has the option of a better one).
Though in a world where “eventual consistency” is accepted, may be “eeny, meeny, miny, moe” will be more generally considered OK at some point :)
At least SQLite tries to be consistent (taking the value from the row where the aggregate found its value) where that is possible (which it often isn't) which mySQL (which also allows non-grouped non-aggregated columns in the projection list) does not.
Though in a world where “eventual consistency” is accepted, may be “eeny, meeny, miny, moe” will be more generally considered OK at some point :)
At least SQLite tries to be consistent (taking the value from the row where the aggregate found its value) where that is possible (which it often isn't) which mySQL (which also allows non-grouped non-aggregated columns in the projection list) does not.