One of the things that I’m the most excited about in “Denali” CTP3 is the enhancements to the OVER clause. One of the things that I’m particularly excited about is the addition of the ROWS/RANGE clause support. One of the reasons that I’m excited about this is that this provides a supported, documented (in BOL) way to perform running totals.
My current favorite method of performing running totals is using the so-called “Quirky Update” / “Pseudo-Cursor” method. However, there is plenty of controversy surrounding the use of this method, primarily centered around the need for following a list of rules – rules that are not documented in BOL. (Please see this article for how to perform running totals using the Quirky Update method and for the rules necessary to achieve the proper results.)
Now that running totals are supported in “Denali” CTP3, I decided to test out the various methods of doing so. Using the environment setup and test code from the above article, I added the various methods of performing running totals available in “Denali” CTP3. (Code reprinted with permission of Jeff Moden.)
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/* /************************************************************************************* Create the test table with a non-clustered Primary Key and a separate clustered index This code has been tested in SQL Server 2000 and 2005. *************************************************************************************/ --===== Do this testing in a nice, "safe" place that everyone has USE TempDB GO --===== If the test table already exists, drop it in case we need to rerun. -- The 3 part naming is overkill, but prevents accidents on real tables. IF OBJECT_ID('TempDB.dbo.TransactionDetail') IS NOT NULL DROP TABLE TempDB.dbo.TransactionDetail GO --===== Create the test table (TransactionDetail) with a NON clustered PK CREATE TABLE dbo.TransactionDetail ( TransactionDetailID INT IDENTITY(1,1), --Temporal "tie-breaker" Date DATETIME, AccountID INT, Amount MONEY, AccountRunningTotal MONEY, --Running total across each account AccountRunningCount INT, --Like "Rank" across each account NCID INT, --For "proof" later in the article CONSTRAINT PK_TransactionDetail_TransactionDetailID PRIMARY KEY NONCLUSTERED (TransactionDetailID) WITH FILLFACTOR = 100 ) GO --===== Add a clustered index that will easily cause page splits because -- of the randomized data being inserted. This index also represents -- the expected sort order of most of the code examples. CREATE CLUSTERED INDEX IXC_Transaction_AccountID_Date_TransactionDetailID ON dbo.TransactionDetail (AccountID, Date, TransactionDetailID) --===== Add a non-clustered index on the NCID column sorted in -- descending order. This is for some "proofs" later on -- in the article. CREATE NONCLUSTERED INDEX IX_Transaction_NCID ON dbo.TransactionDetail (NCID DESC) GO /************************************************************************************* Populate the table using a rather slow method but one that's sure to cause lots of Page splits and that will fragment the table with over 99% fragmentation. *************************************************************************************/ --===== Preset the environment for appearance and speed SET NOCOUNT ON --===== Populate the table in "segments" to force page splits. -- Normally this would NOT have a While loop in it. -- Because the While loop is there and page splits are happening, -- this takes a whopping 00:02:50 to create on my box. WHILE (ISNULL(IDENT_CURRENT('TransactionDetail'),0)) < 1000000 BEGIN INSERT INTO dbo.TransactionDetail (Date, AccountID, Amount) SELECT TOP 10000 --10 years worth of dates with times from 1/1/2000 to 12/31/2009 CAST(RAND(CHECKSUM(NEWID()))*3653.0+36524.0 AS DATETIME) AS Date, --100 different account numbers ABS(CHECKSUM(NEWID()))%100+1, --Dollar amounts from -99.99 to + 99.99 CAST(CHECKSUM(NEWID())%10000 /100.0 AS MONEY) FROM Master.dbo.SysColumns sc1 CROSS JOIN Master.dbo.SysColumns sc2 END --===== Update the NCID column to be the reverse of the TransactionDetailID column UPDATE dbo.TransactionDetail SET NCID = 1000000 - TransactionDetailID + 1 GO USE TEMPDB GO CREATE PROCEDURE dbo.Verify AS /************************************************************************************* Code to verify that the account running total calculation worked correctly. Please read the comments to see how it works. *************************************************************************************/ --===== Conditionally drop the verification table to make -- it easy to rerun the verification code IF OBJECT_ID('TempDB..#Verification') IS NOT NULL DROP TABLE dbo.#Verification --===== Define a variable to remember the number of rows -- copied to the verification table DECLARE @MyCount INT --===== Copy the data from the test table into the -- verification table in the correct order. -- Remember the correct order with an IDENTITY. SELECT IDENTITY(INT,1,1) AS RowNum, AccountID, Amount, AccountRunningTotal INTO #Verification FROM dbo.TransactionDetail ORDER BY AccountID, Date, TransactionDetailID --===== Remember the number of rows we just copied SELECT @MyCount = @@ROWCOUNT --===== Check the running total calculations SELECT CASE WHEN COUNT(hi.RowNum) + 1 = @MyCount THEN 'Account Running Total Calculations are correct' ELSE 'There are some errors in the Account Running Totals' END FROM #Verification lo INNER JOIN #Verification hi ON lo.RowNum + 1 = hi.RowNum WHERE (-- Compare lines with the same AccountID hi.AccountID = lo.AccountID AND hi.AccountRunningTotal = lo.AccountRunningTotal + hi.Amount) OR (-- First line of account has running total same as amount hi.AccountID <> lo.AccountID AND hi.AccountRunningTotal = hi.Amount) GO /************************************************************************************** This stored procedure will clear the calculated columns in the test table without disturbing the randomized data in the table so that we can repeat tests and use different methods without changing the test data. **************************************************************************************/ USE TEMPDB GO CREATE PROCEDURE dbo.ResetTestTable AS UPDATE dbo.TransactionDetail SET AccountRunningTotal = NULL, AccountRunningCount = NULL GO */ /************************************************************************************* Pseduo-cursor update using the "Quirky Update" to calculate both Running Totals and a Running Count that start over for each AccountID. Takes 24 seconds with the INDEX(0) hint and 6 seconds without it on my box. *************************************************************************************/ --===== Supress the auto-display of rowcounts for speed an appearance SET NOCOUNT ON -- Quirky Update running totals --===== Declare the working variables DECLARE @PrevAccountID INT DECLARE @AccountRunningTotal MONEY DECLARE @AccountRunningCount INT --===== Update the running total and running count for this row using the "Quirky -- Update" and a "Pseudo-cursor". The order of the UPDATE is controlled by the -- order of the clustered index. UPDATE dbo.TransactionDetail SET @AccountRunningTotal = AccountRunningTotal = CASE WHEN AccountID = @PrevAccountID THEN @AccountRunningTotal + Amount ELSE Amount END, @AccountRunningCount = AccountRunningCount = CASE WHEN AccountID = @PrevAccountID THEN @AccountRunningCount + 1 ELSE 1 END, @PrevAccountID = AccountID FROM dbo.TransactionDetail WITH (TABLOCKX) OPTION (MAXDOP 1) GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals using DEFAULT RANGE option ; WITH cte AS ( SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID) FROM dbo.TransactionDetail ) UPDATE cte SET AccountRunningTotal = ART, AccountRunningCount = ARC GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals subquery using DEFAULT RANGE option -- this is the same as the cte method ; UPDATE target SET AccountRunningTotal = ART, AccountRunningCount = ARC FROM (SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID) FROM dbo.TransactionDetail ) target GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals with self-join using DEFAULT RANGE option. ; WITH cte AS ( SELECT TransactionDetailID, [Date], AccountID, Amount, AccountRunningTotal = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID), AccountRunningCount = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID), NCID FROM dbo.TransactionDetail ) UPDATE td SET AccountRunningTotal = cte.AccountRunningTotal, AccountRunningCount = cte.AccountRunningCount FROM dbo.TransactionDetail td JOIN cte ON cte.TransactionDetailID = td.TransactionDetailID GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals using ROWS UNBOUNDED PRECEDING ; WITH cte AS ( SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID ROWS UNBOUNDED PRECEDING), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID ROWS UNBOUNDED PRECEDING) FROM dbo.TransactionDetail ) UPDATE cte SET AccountRunningTotal = ART, AccountRunningCount = ARC GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals using RANGE UNBOUNDED PRECEDING ; WITH cte AS ( SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID RANGE UNBOUNDED PRECEDING), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID RANGE UNBOUNDED PRECEDING) FROM dbo.TransactionDetail ) UPDATE cte SET AccountRunningTotal = ART, AccountRunningCount = ARC GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals using ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ; WITH cte AS ( SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) FROM dbo.TransactionDetail ) UPDATE cte SET AccountRunningTotal = ART, AccountRunningCount = ARC GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals using RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ; WITH cte AS ( SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) FROM dbo.TransactionDetail ) UPDATE cte SET AccountRunningTotal = ART, AccountRunningCount = ARC GO EXEC dbo.Verify GO EXEC dbo.ResetTestTable GO -- DENALI CTP3 Running Totals using ROWS BETWEEN 2147483647 PRECEDING AND CURRENT ROW ; WITH cte AS ( SELECT AccountRunningTotal, AccountRunningCount, ART = SUM(Amount) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID ROWS BETWEEN 2147483647 PRECEDING AND CURRENT ROW), ARC = SUM(1) OVER (PARTITION BY AccountID ORDER BY Date, TransactionDetailID ROWS BETWEEN 2147483647 PRECEDING AND CURRENT ROW) FROM dbo.TransactionDetail ) UPDATE cte SET AccountRunningTotal = ART, AccountRunningCount = ARC GO EXEC dbo.Verify GO |
And the results, as shown in Profiler, are:
(Click the image to view the full Profiler screen.)
When performing the running totals with the new OVER clause enhancements in “Denali”, it has 3 million to 18 million reads, vs. 8 thousand for the Quirky Update. This difference is reflected in the time each takes: the OVER clause enhancements take 22 – 75 seconds to perform the running totals, while the Quirky Update performs it in 3.5 seconds.
Let’s hope that all of this is due to it being in a beta state and that it will improve when it reaches RTM. When it does reach the RTM status, I’ll test again to decide which method I’ll use. My impression right now is that it looks like I’ll be keeping the Quirky Update in my toolbag for a long time when performing running totals.
Update: 2014-01-30
Well, it’s been a while since SQL 2012 went to RTM, so I finally decided to rerun this performance test. I’ve waited so long, it’s actually running on SQL 2012 SP1. (And, my hardware has been upgraded, which you will notice with the improved times). The 2012 performance results are:
| TextData | CPU | Reads | Writes | Duration | Rank by Duration |
|---|---|---|---|---|---|
| Quirky Update running totals | 1,623 | 8,764 | 0 | 1,675 | 1 |
| SQL 2012 SP1 running totals using DEFAULT RANGE option | 24,773 | 17,943,842 | 4,005 | 26,018 | 7 |
| SQL 2012 SP1 running totals subquery using DEFAULT RANGE option | 25,334 | 17,943,846 | 4,013 | 26,556 | 8 |
| SQL 2012 SP1 running totals with self-join using DEFAULT RANGE option | 23,289 | 12,053,268 | 4,159 | 17,226 | 4 |
| SQL 2012 SP1 running totals using ROWS UNBOUNDED PRECEDING | 13,120 | 8,902,436 | 0 | 13,714 | 2 |
| SQL 2012 SP1 running totals using RANGE UNBOUNDED PRECEDING | 24,897 | 17,943,908 | 4,125 | 25,945 | 6 |
| SQL 2012 SP1 running totals using ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW | 13,292 | 8,902,440 | 0 | 13,930 | 3 |
| SQL 2012 SP1 running totals using RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW | 24,461 | 17,943,851 | 4,056 | 25,899 | 5 |
| SQL 2012 SP1 Running Totals using ROWS BETWEEN 2147483647 PRECEDING AND CURRENT ROW | 27,971 | 17,882,461 | 10,224 | 29,210 | 9 |
As you can see, the Quirky Update still blows the other methods away. However, the OVER() clause enhancements are still way better than a cursor, or even a self-join. So, my recommendation is to use the OVER() clause, unless you need the extra performance boost of the Quirky Update. This is based solely upon the need to follow undocumented rules for the Quirky Update. Testing will reveal which method you need to use.
Something that you may notice in the results: all of these tests are updating a table with the running total. So how is it that the Quirky Update and the next two fastest means have zero writes? I’ve noticed this before and I filed a connect item about it, which Microsoft has decided that they won’t fix (not enough people affected). If you would like to see this fixed, please go vote for this connect item.
