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Dynamic PIVOT CLR Expand / Collapse
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Posted Wednesday, December 5, 2012 9:28 PM
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Comments posted to this topic are about the item Dynamic PIVOT CLR
Post #1393313
Posted Thursday, December 6, 2012 5:07 AM
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Very nice article.

A question:
Is it possible for me to for example create a Class, generate a List of that class, populate it with the SQL Server query information, after that use LINQ to manipulate the information in this List and after return the content of this list on the procedure?

Thanks a lot.
Post #1393443
Posted Thursday, December 6, 2012 7:13 AM
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It's good, but it still doesn't resolve the biggest problem with SQL's PIVOT functionality (which is no fault of yours), which is that there is no way to create a dynamic pivot result-set that you can join to.

For example, if you could create a dynamic pivot in a table valued function then you could join to the function, but there isn't a way to create a dynamic pivot UDF.

PIVOT would be a heck of a lot more powerful if you could do that...
Post #1393510
Posted Thursday, December 6, 2012 7:21 AM


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Good article.

I do want to point out that dynamic pivots, especially for things like "rolling date reporting" just aren't difficult to do in SQL Server.


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Post #1393518
Posted Thursday, December 6, 2012 7:38 AM
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I would agree when you are using known and predictable values like a set of dates or even dates that haven't occurred, creating a PIVOT in SQL is quite simple. This exercise was for those types of collections of data that are "dynamic" and ever changing. When you have an unpredictable set of data that you need to pivot, you really have no other choice.
Post #1393526
Posted Thursday, December 6, 2012 7:41 AM
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@rmcomics

I don't see why not as long as your list is either based upon static information or populated from the same connection. Though I imagine if the data that you wanted to integrate into the list were on the same connection, that you would somehow integrate that into the select statement that is passed into the @query parameter.

Perhaps you are just asking in general can you use LINQ within a CLR function? The answer would also be yes.
Post #1393527
Posted Thursday, December 6, 2012 8:11 AM


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Eric Wahner-345205 (12/6/2012)
I would agree when you are using known and predictable values like a set of dates or even dates that haven't occurred, creating a PIVOT in SQL is quite simple. This exercise was for those types of collections of data that are "dynamic" and ever changing. When you have an unpredictable set of data that you need to pivot, you really have no other choice.
Well, no, that's not true, you just have to use dynamic SQL.

Something like this:
/*
Title: ExtProps.spjc_viewExtendedProperties
Author: Jon Crawford
Description: pivots the extended properties that are available in the database
Business Need: to search the db for existing objects
What is the user going to do with this?:
Known flaws: n/a
Revision History:
Date Changes
------ -------
9/13/2012 'initial implementation'
9/13/2012 modified to use dynamic SQL so that if new properties show up, they'll be included

*/

ALTER PROCEDURE [ExtProps].[spjc_viewExtendedProperties] (@searchTerm VARCHAR(255) = NULL)
AS
BEGIN


DECLARE @sql VARCHAR(MAX),
@properties VARCHAR(8000)

--find all the user created extended properties,
--but to force a reasonable order into the view we use a temp table to store distinct values
-- before you use them in the dynamic SQL below

DECLARE @table TABLE (name VARCHAR(255),orderValue int)

INSERT INTO @table (name,orderValue)
SELECT DISTINCT name ,
--here's where we pick the order of columns we want
CASE name
WHEN 'Title' THEN 1
WHEN 'Author' THEN 2
WHEN 'Description' THEN 3
WHEN 'Known Flaws' THEN 4
ELSE 99 --everything else will just show up after these ones, no particular order
END AS orderValue
FROM ExtProps.Properties
--get rid of the Microsoft extended properties
WHERE name NOT IN ('Caption','Long_Description',
'microsoft_database_tools_support',
'MS_Description',
'MS_DiagramPane1',
'MS_DiagramPaneCount')
ORDER BY orderValue

--==============================
-- testing

--SELECT *
--FROM @table AS t
--==============================

--shove the names of all the distinct extended properties into a variable so we can use it in the dynamic SQL
SELECT @properties= COALESCE(@properties ,'')+'['+CONVERT(VARCHAR(255),p.name)+'],'
FROM @table AS p

--get rid of the last comma that we added just above
SET @properties = LEFT(@properties,LEN(@properties)-1)

--==============================
-- testing

--SELECT @properties
--==============================

--force all of the unique property names into our PIVOT statement below,
-- but hard-code the ltrim of the name and value (gets rid of leading blanks which cause ordering issues)
-- and force the order by Title to make it look neat
SET @sql =
'SELECT '+@properties+'
FROM ( SELECT p.class ,
p.class_desc ,
p.object_schema ,
p.object_name ,
p.column_name ,
p.major_id ,
p.minor_id ,
LTRIM(CONVERT(varchar(255),p.name)) AS name ,
LTRIM(CONVERT(varchar(1000),p.value)) AS value
FROM ExtProps.Properties AS p
) AS sourceTable
PIVOT ( MIN(value) FOR [name] IN ( '+@properties+' ) ) AS PivotTable
WHERE pivotTable.Title IS NOT NULL
AND (
pivotTable.Title LIKE ''%'+COALESCE(@searchTerm,'')+'%''
OR pivotTable.Description LIKE ''%'+COALESCE(@searchTerm,'')+'%''
)
ORDER BY [Title]'

--==============================
-- testing

--PRINT @sql
--==============================
--now execute the PIVOT statement we built to return data
EXEC(@SQL)
END

**Edit - I should have had a link in there, in case anyone is wondering, I'm pivoting the extended properties that I populate using Michael Coles' sp's (very handy)

http://sqlblog.com/blogs/michael_coles/archive/2010/01/12/t-sql-tuesday-easy-extended-properties.aspx


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Post #1393545
Posted Thursday, December 6, 2012 8:16 AM
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I've done this loads of time using TSQL sps and dynamic sql within, much in the same way as the CLR routine. Is there an advantage to using CLR over TSQL?
Post #1393547
Posted Thursday, December 6, 2012 9:05 AM
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vopipari (12/6/2012)
I've done this loads of time using TSQL sps and dynamic sql within, much in the same way as the CLR routine. Is there an advantage to using CLR over TSQL?


There are somethings that SQL does quite well and then there are somethings that .NET does well. What my approach attempts to do is simplify it so that you don't have to write a custom procedure for every PIVOT that you do. I too have used dynamic sql to solve this problem as well, and while I haven't done any performance testing to see which one performs better than the other, I can say that there should be fewer trips to the database with the CLR method.

This was more of an educational post to show how it could be done using a CLR procedure. I leave it up to the community to decide if this works for them or not.
Post #1393587
Posted Thursday, December 6, 2012 9:09 AM
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@jcrawf02

I think you confused my point with using a PIVOT vs dynamic PIVOT. When I said you have no choice, I was referring to doing a dynamic PIVOT. If you have unpredictable results you cannot write a PIVOT query without using dynamic sql to select the distinct rows that will ultimately be your columns.
Post #1393592
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