SQL Server中啥样实现数字辅助表
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这篇文章主要介绍SQL Server中怎么样实现数字辅助表的内容，一些朋友可能不是很了解数字辅助表，其实数字辅助表有很大的用处，接下来我们一起来了解看看SQL Server 实现数字辅助表的方法。 数字辅助表是一个连续整数的数列，通常用来实现多种不同的查询任务。大多分两类：足够大物理数字表和表函数，前者可以称为静态的，后者可以称为动态且按需生产。 物理数字表通常存在一个物理表，表记录相对足够大，相关的T-SQL代码如下： IF OBJECT_ID(N'dbo.Nums', 'U') IS NOT NULL BEGIN DROP TABLE dbo.Nums; END GO CREATE TABLE dbo.Nums ( Num INT NOT NULL, CONSTRAINT PK_U_CL_Nums_Num PRIMARY KEY CLUSTERED ( Num ASC ) ); GO INSERT INTO dbo.Nums (Num) SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RowNum FROM master.dbo.spt_values; GO 注意：如何填充物理数字表的方法很多，为了演示作用使用了一种。 测试的T-SQL代码如下： 1 SELECT Num 2 FROM dbo.Nums; 3 GO 表函数实现使用交叉连接和CTE，SQL Server 2005和以上版本的T-SQL代码如下： IF OBJECT_ID(N'dbo.ufn_GetNums', N'IF') IS NOT NULL BEGIN DROP TABLE dbo.ufn_GetNums; END GO --================================== -- 功能: 获取指定范围的数字数列 -- 说明: 交叉最后层级的CTE得到的数据行：在L级（从0开始计数）得到的行的总数为2^2^L。 -- 例如：在5级就会得到4 294 967 596行。5级的CTE提供了超过40亿的行。 -- 作者: XXX -- 创建: yyyy-MM-dd -- 修改: yyyy-MM-dd XXX 修改内容描述 --================================== CREATE FUNCTION dbo.ufn_GetNums ( @bintLow BIGINT, @bintHigh BIGINT ) RETURNS TABLE AS RETURN WITH L0 AS (SELECT c FROM (VALUES(1), (1)) AS LO(c)), L1 AS (SELECT 1 AS c FROM L0 AS T CROSS JOIN L0 AS T2), L2 AS (SELECT 1 AS c FROM L1 AS T CROSS JOIN L1 AS T2), L3 AS (SELECT 1 AS c FROM L2 AS T CROSS JOIN L2 AS T2), L4 AS (SELECT 1 AS c FROM L3 AS T CROSS JOIN L3 AS T2), L5 AS (SELECT 1 AS c FROM L4 AS T CROSS JOIN L4 AS T2), Nums AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RowNum FROM L5) SELECT TOP (@bintHigh - @bintLow + 1) @bintLow + RowNum - 1 AS Num FROM Nums ORDER BY RowNum ASC; GO SQL Server 2012增加了有关分页的新特性，相关的T-SQL代码如下: IF OBJECT_ID(N'dbo.ufn_GetNums2', N'IF') IS NOT NULL BEGIN DROP TABLE dbo.ufn_GetNums2; END GO --================================== -- 功能: 获取指定范围的数字数列 -- 说明: 交叉最后层级的CTE得到的数据行：在L级（从0开始计数）得到的行的总数为2^2^L。 -- 例如：在5级就会得到4 294 967 596行。5级的CTE提供了超过40亿的行。 -- 作者: XXX -- 创建: yyyy-MM-dd -- 修改: yyyy-MM-dd XXX 修改内容描述 --================================== CREATE FUNCTION dbo.ufn_GetNums2 ( @bintLow BIGINT, @bintHigh BIGINT ) RETURNS TABLE AS RETURN WITH L0 AS (SELECT c FROM (VALUES(1), (1)) AS LO(c)), L1 AS (SELECT 1 AS c FROM L0 AS T CROSS JOIN L0 AS T2), L2 AS (SELECT 1 AS c FROM L1 AS T CROSS JOIN L1 AS T2), L3 AS (SELECT 1 AS c FROM L2 AS T CROSS JOIN L2 AS T2), L4 AS (SELECT 1 AS c FROM L3 AS T CROSS JOIN L3 AS T2), L5 AS (SELECT 1 AS c FROM L4 AS T CROSS JOIN L4 AS T2), Nums AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RowNum FROM L5) SELECT @bintLow + RowNum - 1 AS Num FROM Nums ORDER BY RowNum ASC OFFSET 0 ROWS FETCH FIRST @bintHigh - @bintLow + 1 ROWS ONLY; GO 以函数ufn_GetNums为例，演示相关的效果。获取指定范围的数字序列的T-SQL代码如下： SELECT Num FROM dbo.ufn_GetNums(11, 20); GO （编辑：银川站长网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
