SQL Server 怎样生成序列号(虚拟数字辅助表)

</pre><pre name="code" class="sql">--生成一个"序列" 或者说生成一个"虚拟数字辅助表"是扩展数据库集合操作的重要途径。其主要创建途径一般是通过笛卡尔积法、系统表法(实质一般也是笛卡尔积法)、创建自定义函数法等方式。  
  
--笛卡尔积法，先构建一个包含10行记录的辅助表，选择10行记录主要是为了方便交叉连接时按照10进制扩展行数  
WITH t1 AS (  
SELECT 1 AS RN  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
UNION All  
SELECT 1  
)  
SELECT NUM=ROW_NUMBER() OVER(ORDER BY a.RN) FROM T1 a,T1 b,T1 c,T1 d,T1 e,T1 f,T1 g  
--生成e10+8(一千万)耗时01:12  
  
--递归法，递归法另一用途是层次查询遍历各级节点；在实现各种复杂数学序列中亦有应用  
--注意当递归次数过百时需加OPTION(MAXRECURSION 0)控制条件使数据库不限定递归次数  
WITH T1 AS (  
SELECT 1 AS NUM  
UNION ALL  
SELECT T1.NUM+1  
FROM T1  
WHERE T1.NUM<10000000)  
SELECT NUM FROM T1  
OPTION(MAXRECURSION 0)  
--生成e10+8(一千万)耗时02:45  
  
--系统表法，生成0-2047  
SELECT number FROM master..spt_values WHERE type='p'  
  
SELECT TOP 10000000 NUM=ROW_NUMBER() OVER(ORDER BY GETDATE())     
FROM syscolumns a,syscolumns b,syscolumns c  
--生成e10+8(一千万)耗时01:16  
  
--自定义函数法  
-- definition of GetNums function, SQL Server 2012 version  
--注意生成的"虚拟数字辅助表"的列别名是"n"  
USE TSQL2012;  
IF OBJECT_ID('dbo.GetNums', 'IF') IS NOT NULL DROP FUNCTION dbo.GetNums;  
GO  
CREATE FUNCTION dbo.GetNums(@low AS BIGINT, @high AS BIGINT) RETURNS TABLE  
AS  
RETURN  
  WITH  
    L0   AS (SELECT c FROM (VALUES(1),(1)) AS D(c)),  
    L1   AS (SELECT 1 AS c FROM L0 AS A CROSS JOIN L0 AS B),  
    L2   AS (SELECT 1 AS c FROM L1 AS A CROSS JOIN L1 AS B),  
    L3   AS (SELECT 1 AS c FROM L2 AS A CROSS JOIN L2 AS B),  
    L4   AS (SELECT 1 AS c FROM L3 AS A CROSS JOIN L3 AS B),  
    L5   AS (SELECT 1 AS c FROM L4 AS A CROSS JOIN L4 AS B),  
    Nums AS (SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS rownum  
            FROM L5)  
  SELECT @low + rownum - 1 AS n  
  FROM Nums  
  ORDER BY rownum  
  OFFSET 0 ROWS FETCH FIRST @high - @low + 1 ROWS ONLY;  
GO  
  
-- definition of GetNums function, pre-SQL Server 2012 version  
IF OBJECT_ID('dbo.GetNums', 'IF') IS NOT NULL  
  DROP FUNCTION dbo.GetNums;  
GO  
CREATE FUNCTION dbo.GetNums(@low AS BIGINT, @high AS BIGINT) RETURNS TABLE  
AS  
RETURN  
  WITH  
    L0   AS (SELECT c FROM (VALUES(1),(1)) AS D(c)),  
    L1   AS (SELECT 1 AS c FROM L0 AS A CROSS JOIN L0 AS B),  
    L2   AS (SELECT 1 AS c FROM L1 AS A CROSS JOIN L1 AS B),  
    L3   AS (SELECT 1 AS c FROM L2 AS A CROSS JOIN L2 AS B),  
    L4   AS (SELECT 1 AS c FROM L3 AS A CROSS JOIN L3 AS B),  
    L5   AS (SELECT 1 AS c FROM L4 AS A CROSS JOIN L4 AS B),  
    Nums AS (SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS rownum  
            FROM L5)  
  SELECT TOP(@high - @low + 1) @low + rownum - 1 AS n  
  FROM Nums  
  ORDER BY rownum;  
GO  
  
-- test function  
--生成e10+8(一千万)耗时01:18  
SELECT n FROM dbo.GetNums(1, 10000000);  
  
--生成11至20的序列  
SELECT n FROM dbo.GetNums(11, 20);  
  
--用函数生成日期序列，注意日期序列可由递归法直接生成，但日期类型必须是datetime，不能是date类型  
DECLARE   
  @start AS DATE = '20120201',  
  @end   AS DATE = '20120212';  
SELECT DATEADD(day, n, @start) AS dt  
FROM dbo.GetNums(0, DATEDIFF(day, @start, @end)) AS Nums;  
GO  
  
DECLARE   
  @start AS DATETIME2 = '2012-02-12 00:00:00.0000000',  
  @end   AS DATETIME2 = '2012-02-18 12:00:00.0000000';  
SELECT DATEADD(hour, n*12, @start) AS dt  
FROM dbo.GetNums(0, DATEDIFF(hour, @start, @end)/12) AS Nums;  
GO  
[sql] view plain copy
--T-SQL  
CREATE TABLE #NumberSequense(RN INT);  
DECLARE @i int;   
SET @i = 1  
  
WHILE @i <= 1000  
BEGIN   
INSERT INTO #NumberSequense  
SELECT @i;  
SET @i = @i + 1  
END  
  
SELECT *   
  FROM #NumberSequense  
 ORDER BY RN  
DROP TABLE #NumberSequense;  

--T-SQL  
CREATE TABLE #NumberSequense(RN INT);  
DECLARE @i int;   
SET @i = 1  
  
WHILE @i <= 1000  
BEGIN   
INSERT INTO #NumberSequense  
SELECT @i;  
SET @i = @i + 1  
END  
  
SELECT *   
  FROM #NumberSequense  
 ORDER BY RN  
DROP TABLE #NumberSequense;