Question

I need to model an idea which can be broken down and thought of as follows:

1. BookDetails
2. BookPrices

The problem here is that you can have many prices for books and these prices are likely to change. Here’s an example

BookDetails:
-----------------
ID  Name
1   Harry Potter…

This is easy enough.

Where it is more interesting is that for this one book I might have ten different prices on that day, e.g.:

BookPrices:
------------------------------------
Book_Details_Id  Kind          Price
1                SpecialOffer     10
1                BulkPurchase     20
1                Normal           30

I need to provide a list of books and all their prices in columns – something like:

BookName         SpecialOffer   BulkPurchase      Normal    
Harry Potter…              10             20          30

My question is: Should the book price table actually have all the different price types as columns? To me this is ugly and a better idea is to have each price as a row

If I use that approach I cannot think of a SQL query to generate me the result set. I have been thinking about this all morning.

EDIT: I have no leeway on calculating prices – they have to be stored down.

EDIT: This is basically the 1-n appraoch I can think of (Thanks to comment below) – Its what I actually had in mind

SELECT book.bookid, bp1.price, bp2.price FROM book JOIN bookprice bp1 JOIN bookprice bp2 ON bp1.bookid = book.bookid AND bp1.pricetype=1 AND bp2.bookid = book.bookid AND bp2.pricetype=2…

The problem is for ten prices you will be joining ten times which stinks!

Answer 1

This answer is t-SQL specific, and could use a little refinement, but it works on SQL 2005.

Uncomment the commented lines and it’ll update like MAGIC! (okay, not magic, but niftily hacky)

DROP TABLE Books
DROP TABLE Prices
DROP TABLE bookpricing

CREATE TABLE Books ( id INT, title VARCHAR(20) )
CREATE TABLE Prices ( id INT, [desc] VARCHAR(20), pricingchange VARCHAR(20))
CREATE TABLE bookpricing ( id INT, bookid INT, priceid INT, bookprice MONEY )

INSERT INTO Books VALUES (1, 'Hi Mom')
--INSERT INTO Books Values (2, 'This is another book') 
INSERT INTO Prices VALUES (1, 'Standard', '1')
INSERT INTO Prices  VALUES (2, 'Discount', '.5')
INSERT INTO Prices VALUES(3, 'HyperMarkup', '1.5')
INSERT INTO prices VALUES(4, 'Remaindered', '.1')

INSERT INTO BookPricing VALUES (1,1,1,20.00)
INSERT INTO BookPricing VALUES (2,1,2,10.00)
INSERT INTO BookPricing VALUES (3,1,3,30.00)
--INSERT INTO BookPricing VALUES (4,2,1,30.00)
--INSERT INTO BookPricing VALUES (5,2,2,15.00)
--INSERT INTO BookPricing VALUES (6,2,4,3.00)

SELECT * FROM bookpricing 

/** this bit stolen from http://www.tsqltutorials.com/pivot.php **/

DECLARE @columns VARCHAR(max)

SELECT @columns = COALESCE(@columns + ',[' + cast(id as varchar) + ']',
'[' + cast(id as varchar)+ ']')
FROM prices


DECLARE @query VARCHAR(max)

SET @query = '
SELECT * FROM (SELECT BookID, PriceID, BookPrice FROM BookPricing) AS BookTable PIVOT (SUM(bookprice) FOR priceid 
IN (' + @columns + ')
)
AS p'

EXECUTE(@query)