it say that we kill a process (ok it's not a SQL command (COM_QUERY))

in few less words...

we could add a SQL command to KILL ID <query id> (nice! we don't need thread id + query id, i like some redundant information to make my self more secure :P, but since query id can be a 64bits value i think i will not have time to overflow the query id and get the same query id in less than 1 second)

and we could add a new protocol command (i don't know if it's nice... because add this is incompatible with mysql protocol, and probably will only work with mariadb client library...), but, if we want to add it, could be nice add a new parameter (optional) about the query id, instead of only KILL and thread_id, add a KILL null (or 0 if thread id can't be 0), and a query id, to KILL protocol