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Friday, August 26, 2005

SQL: Efficient Sequential Number Table Function

Starting with the Microsoft article from Dr. Tom's Workshop: Generating Sequence Numbers, I modified the code to fit our SQL standards, gave it (what I think is) a more logical name and added a @Min parameter. Figuring out how to properly increment the values when the table didn't start at 1 and handling values near the limits of int was a bit tricky...

--Creates a table of sequential numbers, useful for all sorts of things
--Created 08/26/05 by Oskar Austegard from article at 
--http://msdn.microsoft.com/library/en-us/dnsqlpro03/html/sp03k1.asp
--Limits: @Min and @Max must be between -2147483647 and 2147483647, including.
--If @Max <= @Min, only a single record with @Min is created
ALTER FUNCTION dbo.NumberTable (@Min int, @Max int) 
RETURNS @T TABLE (Number int NOT NULL PRIMARY KEY)
AS
BEGIN
  -- Seed the table with the min value
  INSERT @T VALUES (@Min)
  --Loop until all the rows are created, inserting ever more records for each iteration (1, 2, 4, etc)
  WHILE @@ROWCOUNT > 0
  INSERT @T 
  --Get the next values by adding the current max - start value + 1 to each existing number
  --need to calculate increment value first to avoid arithmetic overflow near limits of int
  SELECT t.Number + (x.MaxNumber - @Min + 1)
  FROM @T t
    CROSS JOIN (SELECT MaxNumber = MAX(Number) FROM @T) x --Current max
  WHERE
    --Do not exceed the Max - shift the increment to the right side to take advantage of index
    t.Number <= @Max - (x.MaxNumber - @Min + 1)
  RETURN
END

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