SELECT * FROM (

SELECT province, count(order_id) AS order_count, sum(item_count) AS item_count
 FROM product_order AS po 
  LEFT JOIN account AS a USING(account_id) 
  LEFT JOIN user_roles AS ur ON (a.login=ur.user_name) 
  WHERE (a.login NOT IN ('client', 'test')) AND (role_name='ADMIN')
  GROUP BY province
) AS o

LEFT JOIN (

SELECT province, count(client_id) AS session_count, sum(length) AS sessions_length
                FROM client AS cl 
                LEFT JOIN account AS a USING(account_id) 
                LEFT JOIN user_roles AS ur ON a.login=ur.user_name 
                WHERE (a.login NOT IN ('client', 'test')) AND (role_name='ADMIN')
         GROUP BY province 
) AS cl USING(province)

  LEFT JOIN account AS a USING(account_id) 
  LEFT JOIN user_roles AS ur ON (a.login=ur.user_name) 
  WHERE (a.login NOT IN ('client', 'test')) AND (role_name='ADMIN')