text: use northwind;
  
  SELECT 
      week_id AS 'Week',
      last_name AS 'Last Name',
      first_name AS 'First Name',
      FORMAT(IFNULL(sales, 0), 2) AS 'Total Sales'
  FROM
      (SELECT 
          e.id AS employee_id, week_id, last_name, first_name
      FROM
          employees e
      CROSS JOIN (SELECT DISTINCT
          (WEEK(order_date)) AS week_id
      FROM
          orders) AS distict_weeks) AS order_weeks
          LEFT OUTER JOIN
      (SELECT 
          employee_id,
              WEEK(order_date) AS order_week,
              SUM(shipping_fee + (quantity * list_price)) AS sales
      FROM
          orders, order_details, products
      WHERE
          orders.id = order_details.order_id
              AND order_details.product_id = products.id
      GROUP BY 1 , 2) AS order_data ON order_weeks.employee_id = order_data.employee_id
          AND order_weeks.week_id = order_data.order_week
  ORDER BY 1 , 2;   
  
  
  SELECT 
      e.id AS employee_id, week_id, last_name, first_name
  FROM
      employees e
          CROSS JOIN
      (SELECT DISTINCT
          (WEEK(order_date)) AS week_id
      FROM
          orders) AS distict_weeks;
          
          
  SELECT DISTINCT
      (WEEK(order_date)) AS week_id
  FROM
      orders;
          
          
  SELECT 
      employee_id,
      WEEK(order_date) AS order_week,
      SUM(shipping_fee + (quantity * list_price)) AS sales
  FROM
      orders,
      order_details,
      products
  WHERE
      orders.id = order_details.order_id
          AND order_details.product_id = products.id
  GROUP BY 1 , 2;      
          
          
  