I am not sure what type of performance you are looking for, but if CLR or external app is not an option, a cursor is all that is left. On my aged laptop I get through 1,000,000 rows in about 100 seconds using the following solution. The nice thing about it is that it scales linearly, so I would be looking at a little about 20 minutes to run through the entire thing. With a decent server you will be faster, but not an order of magnitude, so it would still take several minutes to complete this. If this is a one off process, you probably can afford the slowness. If you need to run this as a report or similar regularly, you might want to store the values in the same table un update them as new rows get added, e.g. in a trigger.
Anyway, here is the code:
IF OBJECT_ID('dbo.MyTable') IS NOT NULL DROP TABLE dbo.MyTable;
CREATE TABLE dbo.MyTable(
Id INT IDENTITY(1,1) PRIMARY KEY CLUSTERED,
v NUMERIC(5,3) DEFAULT ABS(CHECKSUM(NEWID())%100)/100.0
);
MERGE dbo.MyTable T
USING (SELECT TOP(1000000) 1 X FROM sys.system_internals_partition_columns A,sys.system_internals_partition_columns B,sys.system_internals_partition_columns C,sys.system_internals_partition_columns D)X
ON(1=0)
WHEN NOT MATCHED THEN
INSERT DEFAULT VALUES;
--SELECT * FROM dbo.MyTable
DECLARE @st DATETIME2 = SYSUTCDATETIME();
DECLARE cur CURSOR FAST_FORWARD FOR
SELECT Id,v FROM dbo.MyTable
ORDER BY Id;
DECLARE @id INT;
DECLARE @v NUMERIC(5,3);
DECLARE @running_total NUMERIC(6,3) = 0;
DECLARE @bucket INT = 1;
CREATE TABLE #t(
id INT PRIMARY KEY CLUSTERED,
v NUMERIC(5,3),
bucket INT,
running_total NUMERIC(6,3)
);
OPEN cur;
WHILE(1=1)
BEGIN
FETCH NEXT FROM cur INTO @id,@v;
IF(@@FETCH_STATUS <> 0) BREAK;
IF(@running_total + @v > 1)
BEGIN
SET @running_total = 0;
SET @bucket += 1;
END;
SET @running_total += @v;
INSERT INTO #t(id,v,bucket,running_total)
VALUES(@id,@v,@bucket, @running_total);
END;
CLOSE cur;
DEALLOCATE cur;
SELECT DATEDIFF(SECOND,@st,SYSUTCDATETIME());
SELECT * FROM #t;
GO
DROP TABLE #t;
It drops and recreates the table MyTable, fills it with 1000000 rows and then goes to work.
The cursor copies each row into a temp table while running the calculations. At the end the select returns the calculated results. You might be a little faster if you don't copy the data around but do an in-place update instead.
If you have an option to upgrade to SQL 2012 you can look at the new window-spool supported moving window aggregates, that should give you better performance.
On a side note, if you have an assembly installed with permission_set=safe, you can do more bad stuff to a server with standard T-SQL than with the assembly, so I would keep working on removing that barrier - You have a good use case here where CLR really would help you.
Best Answer
As the CASE operation is being applied to each row, checking the sum doesn't make sense logically. What we need to do for each row is check the value, if it's above 500 then sum it, else treat the value as 0.
The above code should accomplish this.