select CLIENT_SOURCE, count(*) as CLIENT_COUNT
from
(
  select distinct player.USER_ID, player.CLIENT_SOURCE
  from wesnothd_game_info game, wesnothd_game_player_info player
  where YEAR(game.START_TIME) = YEAR(CURRENT_DATE - INTERVAL 1 MONTH)
    and MONTH(game.START_TIME) = MONTH(CURRENT_DATE - INTERVAL 1 MONTH)
    and game.END_TIME is not NULL
    and TIMESTAMPDIFF(MINUTE, game.START_TIME, game.END_TIME) > 5
    and player.USER_ID != -1
    and game.INSTANCE_UUID = player.INSTANCE_UUID
    and game.GAME_ID = player.GAME_ID
    and player.CLIENT_SOURCE != ''
) src
group by CLIENT_SOURCE
order by COUNT(*) desc