Product price comparison in sql - sql

Question

I have a table looks like given below query, I add products price in this table daily, with different sellers name :
create table Product_Price
(
id int,
dt date,
SellerName varchar(20),
Product varchar(10),
Price money
)
insert into Product_Price values (1, '2012-01-16','Sears','AA', 32)
insert into Product_Price values (2, '2012-01-16','Amazon', 'AA', 40)
insert into Product_Price values (3, '2012-01-16','eBay','AA', 27)
insert into Product_Price values (4, '2012-01-17','Sears','BC', 33.2)
insert into Product_Price values (5, '2012-01-17','Amazon', 'BC',30)
insert into Product_Price values (6, '2012-01-17','eBay', 'BC',51.4)
insert into Product_Price values (7, '2012-01-18','Sears','DE', 13.5)
insert into Product_Price values (8, '2012-01-18','Amazon','DE', 11.1)
insert into Product_Price values (9, '2012-01-18', 'eBay','DE', 9.4)
I want result like this for n number of sellers(As more sellers added in table)
DT PRODUCT Sears[My Site] Amazon Ebay Lowest Price
1/16/2012 AA 32 40 27 Ebay
1/17/2012 BC 33.2 30 51.4 Amazon
1/18/2012 DE 7.5 11.1 9.4 Sears

Answer 1

I think this is what you're looking for.
SQLFiddle
It's kind of ugly, but here's a little breakdown.
This block allows you to get a dynamic list of your values. (Can't remember who I stole this from, but it's awesome. Without this, pivot really isn't any better than a big giant case statement approach to this.)
DECLARE #cols AS VARCHAR(MAX)
DECLARE #query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' +
QUOTENAME(SellerName)
FROM Product_Price
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
, 1, 1, '')
Your #cols variable comes out like so:
[Amazon],[eBay],[Sears]
Then you need to build a string of your entire query:
select #query =
'select piv1.*, tt.sellername from (
select *
from
(select dt, product, SellerName, sum(price) as price from product_price group by dt, product, SellerName) t1
pivot (sum(price) for SellerName in (' + #cols + '))as bob
) piv1
inner join
(select t2.dt,t2.sellername,t1.min_price from
(select dt, min(price) as min_price from product_price group by dt) t1
inner join (select dt,sellername, sum(price) as price from product_price group by dt,sellername) t2 on t1.min_price = t2.price) tt
on piv1.dt = tt.dt
'
The piv1 derived table gets you the pivoted values. The cleverly named tt derived table gets you the seller who has the minimum sales for each day.
(Told you it was kind of ugly.)
And finally, you run your query:
execute(#query)
And you get:
DT PRODUCT AMAZON EBAY SEARS SELLERNAME
2012-01-16 AA 40 27 32 eBay
2012-01-17 BC 30 51.4 33.2 Amazon
2012-01-18 DE 11.1 9.4 13.5 eBay
(sorry, can't make that bit line up).
I would think that if you have a reporting tool that can do crosstabs, this would be a heck of a lot easier to do there.

Answer 2

The problem is this requirement:
I want result like this for n number of sellers
If you have a fixed, known number of columns for your results, there are several techniques to PIVOT your data. But if the number of columns is not known, you're in trouble. The SQL language really wants you to be able to describe the exact nature of the result set for the select list in terms of the number and types of columns up front.
It sounds like you can't do that. This leaves you with two options:
Query the data to know how many stores you have and their names, and then use that information to build a dynamic sql statement.
(Preferred option) Perform the pivot in client code.

Answer 3

This is something that would probably work well with a PIVOT. Microsoft's docs are actually pretty useful on PIVOT and UNPIVOT.
http://technet.microsoft.com/en-us/library/ms177410(v=sql.105).aspx
Basically it allows you to pick a column, in your case SellerName, and pivot that out so that the elements of the column themselves become columns in the new result. The values that go in the new "Ebay", "Amazon", etc. columns would be an aggregate that you choose - in this case the MAX or MIN or AVG of the price.
For the final "Lowest Price" column you'd likely be best served by doing a subquery in your main query which finds the lowest value per product/date and then joining that back in to get the SellerName. Something like:
SELECT
Product_Price.Date
,Product_Price.Product
,Product_Price.MinimumSellerName
FROM
(SELECT
MIN(Price) AS min_price
,Product
,Date
FROM Product_Price
GROUP BY
Product
,Date) min_price
INNER JOIN Product_Price
ON min_price.Product = Product_Price.Product
AND min_price.Date = Product_Price.Date
Then just put the pivot around that and include the MinimumSellerName columnm, just like you include date and product.