Windowing without a partition by or an order by

2

February 21, 2018 by Kenneth Fisher

If you’ve never worked with windowing functions they look something like this:

SELECT name, max(create_date) OVER 
		-- No this isn't meant to make sense
		(PARTITION BY lower(left(name,1)) ORDER BY owner_sid)
FROM sys.databases;

The other day someone mentioned that you could use ROW_NUMBER which requires the OVER clause without either the PARTITION BY or the ORDER BY parts. So let’s try that out.

-- Create a table to test with
CREATE TABLE Windowing (col1 int, col2 int);
INSERT INTO Windowing 
	VALUES (1,1), (1,2), (1,3), (1,4), (1,5)
		,(2,6), (2,7), (2,8), (2,9), (2,10);
GO
-- Test ROW_NUMBER without PARTITION BY or ORDER BY
SELECT ROW_NUMBER() OVER (), *
FROM Windowing;
Msg 4112, Level 15, State 1, Line 16
The function ‘ROW_NUMBER’ must have an OVER clause with ORDER BY.

 
So nope, doesn’t work. But can we get around it?

SELECT ROW_NUMBER() OVER (ORDER BY 1), *
FROM Windowing; 
GO
SELECT ROW_NUMBER() OVER (ORDER BY '1'), *
FROM Windowing; 
GO
SELECT ROW_NUMBER() OVER (ORDER BY DB_ID()), *
FROM Windowing; 
GO

Ok, so you can do it, but it takes some work. No integers, no constants at all, but a function that returns a constant value will do it. Not really sure why you would want to do this, since generally in order for a row number to be useful its done in order of some value. On the other hand, if you absolutely NEED a unique number value per row, don’t have a useful indexed column (a staging table that’s a heap maybe?), and you don’t want to pay for an expensive sort, this could be handy.

Let’s try one more for fun. MAX

SELECT col1, MAX(col2) OVER ()
FROM Windowing;

Now that works! However, now it doesn’t work with a GROUP BY making it less useful.

SELECT col1, MAX(col2) OVER ()
FROM Windowing
GROUP BY col1;
Msg 8120, Level 16, State 1, Line 29
Column ‘Windowing.col2’ is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

 
Unlike a simple MAX of course.

SELECT col1, MAX(col2)
FROM Windowing
GROUP BY col1;

2 thoughts on “Windowing without a partition by or an order by

  1. Erin Brewer says:

    just a safety note, i had a query with an order by on it already which i added a row_number to which was inserting into a temp table (don’t ask why, legacy code). In query window the results looked fine, but when they were inserted into the temp table the order of the row numbers was inconsistent. Had to add the order by to the row_number clause.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 2,423 other followers

Follow me on Twitter

ToadWorld Pro of the Month November 2013
%d bloggers like this: