So it’s T-SQL Tuesday time again and this month it’s hosted by Jes Schultz Borland.
The topic this month is aggregation. Which is a great topic. Real T-SQL topics are my favorite kind. In the past I’ve actually written a couple of posts on the topic of aggregation which would have fit in perfectly this month:
But this month, I want to tell you about the aggregate function PRODUCT().
The PRODUCT() Aggregate Function
Okay, I’m pulling your leg a bit. There is no function defined in T-SQL that is called PRODUCT(). But everything is in place to let you build one without having to resort to CLR aggregate functions. All we need is to do is remember a bit of math. Remember that:
So when ever you would want to write
SELECT PRODUCT(field) FROM SomeTable |
You can feel free to write
SELECT EXP(SUM(LOG(field))) FROM SomeTable |
Examples
Multiplying the first six primes
SELECT EXP(SUM(LOG(num))) as product FROM (VALUES (2),(3),(5),(7),(11),(13)) as NUMS(num) /* product ---------------------- 30030 */ |
The Value of a 2005 U.S. Dollar in 2010
DECLARE @StartYear INT = 2005; DECLARE @EndYear INT = 2010; SELECT EXP(SUM(LOG(1+ (inflationRate/100.0)))) AS ValueOfUSDollarAfterInflation FROM (VALUES (2001, 2.85), (2002, 1.58), (2003, 2.28), (2004, 2.66), (2005, 3.39), (2006, 3.23), (2007, 2.85), (2008, 3.84), (2009, -0.36), (2010, 1.64), (2011, 0.99) ) AS RATES([year], inflationRate) WHERE [year] BETWEEN @StartYear + 1 AND @EndYear /* ValueOfADollarAfterInflation ---------------------------- 1.11653740799858 */ |
More About This Method
I don’t know the first person who came up with this trick (Most likely Napier). With a quick search, I understand that others have written about its implementation in SQL many times before. In fact, I wouldn’t be surprised if this tip comes up again this T-SQL Tuesday. But I post anyway because I like my examples and had fun writing it.
No mention of negatives and zeroes? (I guess inflation multipliers are always positive, so it’s fair enough)
(1 – 2*(COUNT(case when inflationRate < 0 then 1 end) % 2)) * MIN(case when inflationRate = 0 then 0 else 1 end) * EXP(SUM(LOG(ABS(NULLIF(inflationRate,0)))))
All good though – it's nice to be reminded of this stuff.
Rob
Comment by Rob Farley — March 7, 2011 @ 9:13 pm
Thanks Rob,
I left the mention of zeroes and negatives to keen commenters like yourself.
Cheers
Comment by Michael J Swart — March 7, 2011 @ 10:25 pm
Nice, although we did touch it briefly also in this thread
Lightning Fast Hybrid RUNNING TOTAL – Can you slow it down?
Comment by Naomi — March 8, 2011 @ 9:22 pm
Hi Naomi,
Thanks for the link. It’s interesting that it got mentioned by my friend Brad Shulz in that thread.
In my post I linked to a google search above (and fixed the link just now). I was pointing to the search http://www.google.com/search?q=%2B%22EXP+SUM+LOG%22+%2Bsql which shows thousands of people who have discovered this before I did. C’est la vie.
But none of them feature a picture of the Slap Chop guy do they
Comment by Michael J. Swart — March 8, 2011 @ 9:43 pm
Cool stuff, Michael. Thanks for sharing!
Comment by Jes Schultz Borland — March 8, 2011 @ 9:45 pm
The earliest hit I find via google is:
http://planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=159&lngWId=5
Submitted by Umachandar on 7/25/2000 8:42:10 PM
http://www.umachandar.com/
Comment by Erik Eckhardt — March 17, 2011 @ 7:24 pm