Example query

ts k8s | stats s = sum(rate(network.total_bytes_in)) by network.eth0.currently_connected_clients, b = bucket(@timestamp,1hour) | drop s, network.eth0.currently_connected_clients | eval b = false 

This fails with Connection refused
Some queries will succeed even if you group on non-dimension fields, but it's not supported behavior, so we should have a nicer error message if someone attempts to do this