Listing 4: Creating the fn_sudoku Function
IF OBJECT_ID('dbo.fn_sudoku') IS NOT NULL
  DROP FUNCTION dbo.fn_sudoku;
GO
CREATE FUNCTION dbo.fn_sudoku()
  RETURNS @Sudoku TABLE
(
  row INT NOT NULL,
  col INT NOT NULL,
  val INT NOT NULL,
  PRIMARY KEY(row, col, val)
)
AS
BEGIN

  DECLARE @rc AS INT;

  DECLARE @SudokuUnique TABLE
  (
    row INT NOT NULL,
    col INT NOT NULL,
    box INT NOT NULL,
    val INT NOT NULL,
    PRIMARY KEY(row, col),
    UNIQUE(row, val),
    UNIQUE(col, val),
    UNIQUE(box, val)
  );

  DECLARE @SudokuNonUnique TABLE
  (
    row INT NOT NULL,
    col INT NOT NULL,
    box INT NOT NULL,
    val INT NOT NULL,
    PRIMARY KEY(row, col, val)
  );

-- BEGIN CALLOUT A
  INSERT INTO @SudokuUnique(row, col, val, box)
    SELECT row, col, val,
      (row-1)/3*3 + (col-1)/3 + 1
    FROM SudokuInput;
-- END CALLOUT A

-- BEGIN CALLOUT B
  INSERT INTO @SudokuNonUnique(row, col, val, box)
    SELECT R.n AS row, C.n AS col, V.n,
      (R.n-1)/3*3 + (C.n-1)/3 + 1
    FROM Nums AS R, Nums AS C, Nums AS V
    WHERE R.n <= 9
      AND C.n <= 9
      AND V.n <= 9
      AND NOT EXISTS
        (SELECT * FROM SudokuInput AS S
         WHERE S.row = R.n AND S.col = C.n);
-- END CALLOUT B

  SET @rc = @@rowcount;

-- BEGIN CALLOUT C
  WHILE @rc > 0
  BEGIN

    SET @rc =0;

    -- Rules that remove nonfinal values FROM @SudokuNonUnique
    -- Rules that load final values into @SudokuUnique
    -- After each insert/delete, SET @rc = @rc + @@rowcount

  END
-- END CALLOUT C

  INSERT INTO @Sudoku(row, col, val)
    SELECT row, col, val FROM @SudokuUnique
    UNION ALL
    SELECT row, col, val FROM @SudokuNonUnique

  RETURN;
END