Group data by the change of grouping column value in order

Question

With the following data

create table #ph (product int, [date] date, price int)
insert into #ph select 1, \'20120101\', 1
insert into #ph select 1, \'20120102         


        

Answer 1

WITH marked AS (
  SELECT
    *,
  case
   when (lag(price,1,'') over (partition by product order by date_from)) = price
   then 0 else 1
  end is_price_change
  FROM #ph
),
marked_as_group AS
( SELECT m.*,
       SUM(is_price_change) over (PARTITION BY product order by date_from ROWS 
      BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS price_change_group
  FROM marked m
),
SELECT
  product,
  date_from = MIN(date_from),
  date_to   = MAX(date_to),
  price = MIN(price)
FROM marked_as_group 
GROUP BY
  product,
  price_change_group
ORDER BY
  product,
  date_to