Michael J. Swart

June 8, 2011

Forget About PIVOT, You Don’t Need It

Filed under: SQLServerPedia Syndication,Technical Articles — Tags: , , , — Michael J. Swart @ 12:00 pm

Takeaway: Until recently, I was a huge T-SQL PIVOT fan. But the more I think about it, the more I realize that it’s probably better to pivot data anywhere else than to pivot data in SQL Server. I talk about easier and better alternatives to PIVOT. Remember PIVOT is a T-SQL command that was introduced in SQL Server 2005 that lets you return results as pivot tables or more commonly as cross tabulations.

SQL Server 2000 and Earlier

I remember the first time I came across the need for pivot tables. I knew what I needed the data to look like, but I didn’t know what they were called. It didn’t matter, PIVOT wasn’t yet a T-SQL keyword and I couldn’t make use of it any way.

I was asked to write a query that returned data about the number of widgets and their categories. That seems like no problem right? Except I was asked to return the data in a two dimensional grid (with widgets as rows and categories as columns). It was a perfect use case for PIVOT! Except that it wasn’t yet available and so I was forced to write something complicated in T-SQL that used subqueries, CASE statements and other crazy stuff.

The resulting query was at least 100 lines. It looked complicated but it did the trick. I was actually congratulated on my SQL skillz (although in hindsight I shouldn’t have been).

But it got me to thinking. Why was that so hard? I used to think that any reasonable English question can be translated into simple SQL. But here was a big fat hairy counter-example. I eventually came up with an answer: It’s because the requested data has information about different sets of data in the same row.

SQL Server 2005 and Later

Fast forward a few years. I was learning about all the new stuff that SQL Server 2005 could do. And I came across the new PIVOT keyword. I knew immediately what it could do for me. I knew immediately how it was used. And I used it when the results called for it. I never remembered the syntax because I knew I could always look it up.

Eventually I gained a reputation as a SQL know-it-all (whether I deserved it or not) and I started fielding database questions. If any colleagues were struggling to return a cross-table, it was easy to recognize what they were doing and easier to point them to the online docs for PIVOT.

Or Just Let The App Deal With It

But I realized recently that it’s really not necessary. At the database level, I probably don’t have to pivot this. I can ask the question: Do I really need to deliver the data that way – pre-pivoted? Heck No! I can delegate that stuff. It’s actually a lot easier to pivot this data almost anywhere else besides SQL Server.

So in essence I’m giving myself (and you!) permission to forget something: T-SQL’s PIVOT syntax.

Pivot Inside Excel

Say the data is a one-time-only query and you want to include a cross table in a spreadsheet or email. Well Excel’s pivot feature turns out to be dead simple. This pivot functionality is also found in Open Office’s Calc and any other spreadsheet application built this century. Just a couple extra tips:

  • Using the “format as table” feature can save yourself a couple clicks.
  • Find the “Create Pivot Table” feature under the Insert tab.
  • If you’re still having any trouble, I’m sure there’s tons more help here.

Pivot Inside a .Net App

Okay, so say you’re writing some C# and you have a DataTable that you wish were more pivot-y. Ask and ye shall receive:

DataTable Pivot( DataTable dt, DataColumn pivotColumn, DataColumn pivotValue ) {
	// find primary key columns 
	//(i.e. everything but pivot column and pivot value)
	DataTable temp = dt.Copy();
	temp.Columns.Remove( pivotColumn.ColumnName );
	temp.Columns.Remove( pivotValue.ColumnName );
	string[] pkColumnNames = temp.Columns.Cast<DataColumn>()
		.Select( c => c.ColumnName )
		.ToArray();
 
	// prep results table
	DataTable result = temp.DefaultView.ToTable(true, pkColumnNames).Copy();
	result.PrimaryKey = result.Columns.Cast<DataColumn>().ToArray();
	dt.AsEnumerable()
		.Select(r => r[pivotColumn.ColumnName].ToString())
		.Distinct().ToList()
		.ForEach (c => result.Columns.Add(c, pivotColumn.DataType));
 
	// load it
	foreach( DataRow row in dt.Rows ) {
		// find row to update
		DataRow aggRow = result.Rows.Find(
			pkColumnNames
				.Select( c => row[c] )
				.ToArray() );
		// the aggregate used here is LATEST 
		// adjust the next line if you want (SUM, MAX, etc...)
		aggRow[row[pivotColumn.ColumnName].ToString()] = row[pivotValue.ColumnName];
	}
 
	return result;
}

If you know the shape of your data ahead of time, you could have coded this more easily by hard coding column names. But what I’ve given here is a general procedure (It works on most test cases. Error handling and extra testing are left as an exercise for the reader 🙂 ).

Pivot Inside Other B.I. Clients

Most other clients I can think of have even easier pivot features:

  • Reporting Service’s matrix control is a pivot table.
  • Integration Service’s pivot transformation is easy and handy.
  • Analysis Service’s cubes are nothing but a multi-dimensional pivot tables.
  • Other Business Intelligence software is all over this. If your B.I. software can’t do cross-tables or pivot tables, I would ask for your money back.

You don’t need T-SQL’s PIVOT table at all. Forget that stuff…

… Except When You Do Need T-SQL’s PIVOT

Okay, maybe I’m a bit over-zealous there. Here are some reasons why you might want to use T-SQL’s PIVOT tables. They’re not great reasons but I present them any way. You’ll need to know this stuff:

  • when studying for certifications, interviews or other tests,
  • when the application or data destination you’re working with is not suited to pivoting (although nothing comes to mind). Your choice is then PIVOT using T-SQL or not at all.
  • when the data’s destination is the SSMS results pane. That’s fair.
  • when you don’t have control over the app, or the app is too difficult to modify and it’s expecting a cross-table for data.

So for the most part, you can forget about PIVOT syntax. Next week maybe I’ll talk about remembering the syntax for the MERGE statement. In my opinion, SQL’s MERGE statement is a statement worth remembering, but that’s another story.

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