T-SQL Multiple grouping

Question

I have follwing data :

Product Price   StartDate                   EndDate
Apples  4.9     2010-03-01 00:00:00.000     2010-03-01 00:00:00.000
Apples  4.9           


        

Answer 1

My approach.

Data:

create table t ( producte varchar(50), 
                 price money, 
                 start_date date,
                 end_date date);

insert into t values
( 'apple', 4.9, '2012-01-01', '2012-01-01' ),
( 'apple', 4.9, '2012-01-02', '2012-01-02' ),
( 'apple', 8, '2012-01-04', '2012-01-04' ),
( 'cat', 5, '2012-01-01', '2012-01-01' ),
( 'cat', 6, '2012-01-02', '2012-01-02' ),
( 'cat', 6, '2012-01-03', '2012-01-03' );

Query:

with start_dates as (
  select 
    t.producte, t.price, t.start_date, t.end_date, t.start_date as gr_date    
  from 
    t left outer join 
    t t1 on 
        t.price = t1.price and                         --new
        t.producte = t1.producte and
        t.start_date = dateadd(day,1, t1.end_date )
  where t1.producte is null
  union all
  select 
      t.producte, t.price, t.start_date,t. end_date, gr_date
  from
      t inner join 
      start_dates t1 on  
        t.price = t1.price and                         --new
        t.producte = t1.producte and
        t.start_date = dateadd(day,1, t1.end_date )
)
select t.producte, t.price , min( t.start_date ), max( t.end_date )
from start_dates t
group by  t.producte, gr_date  ,t.price

Results:

| PRODUCTE | PRICE |   COLUMN_2 |   COLUMN_3 |
----------------------------------------------
|    apple |   4.9 | 2012-01-01 | 2012-01-02 |
|    apple |     8 | 2012-01-04 | 2012-01-04 |
|      cat |     5 | 2012-01-01 | 2012-01-01 |
|      cat |     6 | 2012-01-02 | 2012-01-03 |

Explanation

This is a recursive CTE expression. Base query take inital dates for each group of prices. Recursive query looks for last data with this price.

Answer 2

Here is a SQLFiddle demo

with t2 as 
(
select t1.*,
(select count(Price) 
  from t 
  where startdate<t1.startdate 
        and Price<>t1.price
        and Product=t1.Product
)
rng  
from t as t1
)
select Product,Price,min(startDate),max(EndDate)  
from t2 group by Product,Price,RNG
order by 3

Answer 3

SELECT  product, price, MIN(start_date), MAX(end_date)
FROM    (
        SELECT  product, price, start_date, end_date,
                ROW_NUMBER() OVER (PARTITION BY product ORDER BY startDate) rn1,
                ROW_NUMBER() OVER (PARTITION BY product, price ORDER BY startDate) rn2
        FROM    mytable
        ) q
GROUP BY
        product, price, rn2 - rn1
ORDER BY
        product, MIN(start_date), price

Answer 4

I believe this is the best-performing solution so far:

WITH Calc AS (
   SELECT *,
      Grp = DateAdd(day, -Row_Number()
         OVER (PARTITION BY Product, Price ORDER BY StartDate), StartDate
      )
   FROM dbo.PriceHistory
)
SELECT Product, Price, FromDate = Min(StartDate), ToDate = Max(StartDate)
FROM Calc
GROUP BY Product, Price, Grp
ORDER BY FromDate;

Try this out yourself

Answer 5

Here's a suggestion: for each row, you must find the maximum previous date for which the price is different and you Group on that. For example, for any line between 2010-03-11 and 2010-03-16, you must retrieve the date 2010-03-10 because this is the maximum previous date for which the price is different (2.5 versus 4.9). The first row(s) will return a null date but that shouldn't be a problem.

However, for a very long table, this kind of query could become very slow. Therefore, if you have some speed problem, you should look into the possibility of adding a column and use a cursor to fill it incrementally: you loop through it by date and each time you see a new price, you change its value. The final Grouping is then trivial.

Here's something:

Select Product, Price, Min(StartDate) as StartDate, PreviousDate from (
    Select product, price, StartDate, (Select max (StartDate) from table_2 t3 where t3.price <> t2.price and t3.StartDate < t2.StartDate and t3.Product = t2.Product) as previousDate
    from table_2 t2) SQ

Group by Product, Price, PreviousDate
Order by PreviousDate