Microsoft SQL Server PIVOT / UNPIVOT Dynamic PIVOT
Example
One problem with the PIVOT query is that you have to specify all values inside the IN selection if you want to see them as columns.
A quick way to circumvent this problem is to create a dynamic IN selection making your PIVOT dynamic.
For demonstration we will use a table Books in a Bookstore’s database. We assume that the table is quite de-normalised and has following columns
Table: Books
-----------------------------
BookId (Primary Key Column)
Name
Language
NumberOfPages
EditionNumber
YearOfPrint
YearBoughtIntoStore
ISBN
AuthorName
Price
NumberOfUnitsSold
Creation script for the table will be like:
CREATE TABLE [dbo].[BookList](
[BookId] [int] NOT NULL,
[Name] [nvarchar](100) NULL,
[Language] [nvarchar](100) NULL,
[NumberOfPages] [int] NULL,
[EditionNumber] [nvarchar](10) NULL,
[YearOfPrint] [int] NULL,
[YearBoughtIntoStore] [int] NULL,
[NumberOfBooks] [int] NULL,
[ISBN] [nvarchar](30) NULL,
[AuthorName] [nvarchar](200) NULL,
[Price] [money] NULL,
[NumberOfUnitsSold] [int] NULL,
CONSTRAINT [PK_BookList] PRIMARY KEY CLUSTERED
(
[BookId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
Now if we need to query on the database and figure out number of books in English, Russian, German, Hindi, Latin languages bought into the bookstore every year and present our output in a small report format, we can use PIVOT query like this
SELECT * FROM
(
SELECT YearBoughtIntoStore AS [Year Bought],[Language], NumberOfBooks
FROM BookList
) sourceData
PIVOT
(
SUM(NumberOfBooks)
FOR [Language] IN (English, Russian, German, Hindi, Latin)
) pivotrReport
Special case is when we do not have a full list of the languages, so we'll use dynamic SQL like below
DECLARE @query VARCHAR(4000)
DECLARE @languages VARCHAR(2000)
SELECT @languages =
STUFF((SELECT DISTINCT '],['+LTRIM([Language])FROM [dbo].[BookList]
ORDER BY '],['+LTRIM([Language]) FOR XML PATH('') ),1,2,'') + ']'
SET @query=
'SELECT * FROM
(SELECT YearBoughtIntoStore AS [Year Bought],[Language],NumberOfBooks
FROM BookList) sourceData
PIVOT(SUM(NumberOfBooks)FOR [Language] IN ('+ @languages +')) pivotrReport' EXECUTE(@query)
