text: .header on
  .mode column
  
  SELECT * FROM (SELECT name, day FROM CUSTOMERS LEFT JOIN RESERVATION USING (customer_id)) AS qwe
      WHERE NOT EXISTS (
          SELECT name, day FROM (SELECT name, day FROM CUSTOMERS LEFT JOIN RESERVATION USING (customer_id) ORDER BY name DESC) AS asd
          WHERE 
              CASE 
                  WHEN qwe.name IS NULL AND asd.name IS NULL
                  THEN 1
                  WHEN qwe.name IS NULL AND asd.name IS NOT NULL
                  THEN 0
                  WHEN qwe.name IS NOT NULL AND asd.name IS NULL
                  THEN 0
                  ELSE qwe.name = asd.name
              END
  );
  
  