T-SQL查询学习笔记——快速生成数字辅助表的几种方法示例代码

junmail

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-- Auxiliry Table of Numbers
---------------------------------------------------------------------
-- Listing 4-8: Creating and Populating Auxiliary Table of Numbers
SET NOCOUNT ON;
GO
IF OBJECT_ID('dbo.Nums') IS NOT NULL
  DROP TABLE dbo.Nums;
GO
CREATE TABLE dbo.Nums(n INT NOT NULL PRIMARY KEY);
DECLARE @max AS INT, @rc AS INT;
SET @max = 1000000;
SET @rc = 1;
INSERT INTO Nums VALUES(1);
WHILE @rc * 2 <= @max
BEGIN
  INSERT INTO dbo.Nums SELECT n + @rc FROM dbo.Nums;
  SET @rc = @rc * 2;
END
INSERT INTO dbo.Nums
  SELECT n + @rc FROM dbo.Nums WHERE n + @rc <= @max;
GO

drop table nums

-- Naive Solution Returning an Auxiliary Table of Numbers
DECLARE @n AS BIGINT;
SET @n = 1000000;
WITH Nums AS
(
  SELECT 1 AS n
  UNION ALL
  SELECT n + 1 FROM Nums WHERE n < @n
)
SELECT n FROM Nums
OPTION(MAXRECURSION 0);
GO
-- Optimized Solution 1
DECLARE @n AS BIGINT;
SET @n = 1000000;
WITH Base AS
(
  SELECT 1 AS n
  UNION ALL
  SELECT n + 1 FROM Base WHERE n < CEILING(SQRT(@n))
),
Expand AS
(
  SELECT 1 AS c
  FROM Base AS B1, Base AS B2
),
Nums AS
(
  SELECT ROW_NUMBER() OVER(ORDER BY c) AS n
  FROM Expand
)
SELECT n FROM Nums WHERE n <= @n
OPTION(MAXRECURSION 0);
GO
-- Optimized Solution 2
DECLARE @n AS BIGINT;
SET @n = 1000000;
WITH
L0   AS(SELECT 1 AS c UNION ALL SELECT 1),
L1   AS(SELECT 1 AS c FROM L0 AS A, L0 AS B),
L2   AS(SELECT 1 AS c FROM L1 AS A, L1 AS B),
L3   AS(SELECT 1 AS c FROM L2 AS A, L2 AS B),
L4   AS(SELECT 1 AS c FROM L3 AS A, L3 AS B),
L5   AS(SELECT 1 AS c FROM L4 AS A, L4 AS B),
Nums AS(SELECT ROW_NUMBER() OVER(ORDER BY c) AS n FROM L5)
SELECT n FROM Nums WHERE n <= @n;
GO
-- Listing 4-9: UDF Returning an Auxiliary Table of Numbers
IF OBJECT_ID('dbo.fn_nums') IS NOT NULL
  DROP FUNCTION dbo.Nums;
GO
CREATE FUNCTION dbo.fn_nums(@n AS BIGINT) RETURNS TABLE
AS
RETURN
  WITH
  L0   AS(SELECT 1 AS c UNION ALL SELECT 1),
  L1   AS(SELECT 1 AS c FROM L0 AS A, L0 AS B),
  L2   AS(SELECT 1 AS c FROM L1 AS A, L1 AS B),
  L3   AS(SELECT 1 AS c FROM L2 AS A, L2 AS B),
  L4   AS(SELECT 1 AS c FROM L3 AS A, L3 AS B),
  L5   AS(SELECT 1 AS c FROM L4 AS A, L4 AS B),
  Nums AS(SELECT ROW_NUMBER() OVER(ORDER BY c) AS n FROM L5)
  SELECT n FROM Nums WHERE n <= @n;
GO
-- Test function
SELECT * FROM dbo.fn_nums(10) AS F;
GO