create table Table1 (ID integer,Day date,Art integer,Cntr integer,Qnty decimal(16, 3))

Insert into Table1 values
(1, '2018-01-28', 88, 8, 10.000),
(2, '2018-01-29', 88, 8, 15.000),
(3, '2018-01-30', 88, 8, 20.000),
(4, '2018-01-30', 11, 5, 15.000),
(5, '2018-01-29', 11, 5, 20.000),
(6, '2018-07-01', 88, 5, 15.000),
(7, '2018-07-02', 88, 5, 20.000),
(8, '2018-07-06', 88, 5, 25.000),
(9, '2018-07-04', 88, 5, 25.000);

WITH dates(date,day) AS 
(
    SELECT DISTINCT CAST(day AS DATE),day
    FROM Table1
),
groups as
(
    SELECT
      ROW_NUMBER() OVER (ORDER BY date) AS rn,
      dateadd(day, -ROW_NUMBER() OVER (ORDER BY date), date) AS grp,day
    FROM dates
)
SELECT
  COUNT(*) AS day,
  MIN(day) AS minDate,
  MAX(day) AS maxDate
FROM groups
GROUP BY grp
ORDER BY 1 DESC, 2 DESC