比如，我要建立一個1，000，000行的數字表：
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;
這種方式非常巧妙，它并不是一個一個的循環(huán)插入，而是一次插入很多行，{1}，{2}，{3，4}，{5，6，7，8}。。。
為什么這樣會快呢？
是因為它節(jié)省了跟比較其他可用解決方案進行比較和記錄這些日志的時間。
然后，作者給了一個CTE的遞歸的解決方案:
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);--為了移除默認100的遞歸限制
有個更優(yōu)的CTE的解決方案，就是先生成很多行，然后用ROW_NUMBER進行計算，再選擇ROW_NUMBER這列的值就可以了。
復制代碼 代碼如下:
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);
利用笛卡爾積進行不斷的累加，達到了22n行。
最后，作者給出了一個函數，用于生成這樣的數字表：
復制代碼 代碼如下:
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
您可能感興趣的文章:- SQLServer用t-sql命令批量刪除數據庫中指定表(游標循環(huán)刪除)
- 如何在SQL Server 2008下輕松調試T-SQL語句和存儲過程
- SQL Server中的T-SQL的基本對象
- SqlServer 2005 T-SQL Query 學習筆記（3）
- SqlServer 2005 T-SQL Query 學習筆記（2）
- SqlServer 2005 T-SQL Query 學習筆記（1)
- SQLServer 2008 新增T-SQL 簡寫語法
- SQL Server 數據庫管理常用的SQL和T-SQL語句
- SQL Server 數據庫管理常用的SQL和T-SQL語句
- SQL Server 數據庫管理常用的SQL和T-SQL語句
- T-sql語句修改SQL Server數據庫邏輯名、數據庫名、物理名的方法
