SQL Server表分区的NULL值问题
SQL Server表分区只支持range分区这一种类型，但是本人觉得已经够用了
虽然MySQL支持四种分区类型：RANGE分区、LIST分区、HASH分区、KEY分区，还支持子分区，但是功能有些欠缺
共同点是MySQL跟SQL Server也有分区对齐的问题，都是水平切分，大家都允许分区列存在NULL值
这次我们测试SQL Server表分区的分区列的NULL值，究竟NULL值是被存放在哪个区间，以前一直没有注意
测试脚本
--1.创建文件组ALTER DATABASE [sss]ADD FILEGROUP [FG_TinyBlog_Id_01]ALTER DATABASE [sss]ADD FILEGROUP [FG_TinyBlog_Id_02]ALTER DATABASE [sss]ADD FILEGROUP [FG_TinyBlog_Id_03]ALTER DATABASE [sss]ADD FILEGROUP [FG_TinyBlog_Id_04]ALTER DATABASE [sss]ADD FILEGROUP [FG_TinyBlog_Id_05]--2.创建文件ALTER DATABASE [sss]ADD FILE(NAME = N'FG_TinyBlog_Id_01_data',FILENAME = N'E:\DataBase\sss\FG_TinyBlog_Id_01_data.ndf',SIZE = 96MB, FILEGROWTH = 24MB )TO FILEGROUP [FG_TinyBlog_Id_01];ALTER DATABASE [sss]ADD FILE(NAME = N'FG_TinyBlog_Id_02_data',FILENAME = N'E:\DataBase\sss\FG_TinyBlog_Id_02_data.ndf',SIZE = 96MB, FILEGROWTH = 24MB )TO FILEGROUP [FG_TinyBlog_Id_02];ALTER DATABASE [sss]ADD FILE(NAME = N'FG_TinyBlog_Id_03_data',FILENAME = N'E:\DataBase\sss\FG_TinyBlog_Id_03_data.ndf',SIZE = 96MB, FILEGROWTH = 24MB )TO FILEGROUP [FG_TinyBlog_Id_03];ALTER DATABASE [sss]ADD FILE(NAME = N'FG_TinyBlog_Id_04_data',FILENAME = N'E:\DataBase\sss\FG_TinyBlog_Id_04_data.ndf',SIZE = 96MB, FILEGROWTH = 24MB )TO FILEGROUP [FG_TinyBlog_Id_04];ALTER DATABASE [sss]ADD FILE(NAME = N'FG_TinyBlog_Id_05_data',FILENAME = N'E:\DataBase\sss\FG_TinyBlog_Id_05_data.ndf',SIZE = 96MB, FILEGROWTH = 24MB )TO FILEGROUP [FG_TinyBlog_Id_05];--3.创建分区函数CREATE PARTITION FUNCTIONFun_TinyBlog_Id(INT) ASRANGE LEFTFOR VALUES(-10,0,1,6)--4.创建分区方案CREATE PARTITION SCHEME[Sch_TinyBlog_Id] ASPARTITION [Fun_TinyBlog_Id]TO([FG_TinyBlog_Id_01],[FG_TinyBlog_Id_02],[FG_TinyBlog_Id_03],[FG_TinyBlog_Id_04],[FG_TinyBlog_Id_05])
插入测试数据
USE [sss]CREATE TABLE TinyBlog(id INT NULL,NAME VARCHAR(100)) ON [Sch_TinyBlog_Id](id)SELECT * FROM TinyBlog ORDER BY id INSERT INTO [dbo].[TinyBlog] ( [id], [NAME] )VALUES ( NULL, -- id - int '3232' -- NAME - varchar(100) )INSERT INTO [dbo].[TinyBlog] ( [id], [NAME] )VALUES ( -2, -- id - int '-2' -- NAME - varchar(100) )INSERT INTO [dbo].[TinyBlog] ( [id], [NAME] )VALUES ( 66, -- id - int '66' -- NAME - varchar(100) )INSERT INTO [dbo].[TinyBlog] ( [id], [NAME] )VALUES ( 0, -- id - int '0' -- NAME - varchar(100) )INSERT INTO [dbo].[TinyBlog] ( [id], [NAME] )VALUES ( -30, -- id - int '-30' -- NAME - varchar(100) )
表数据如下
SELECT * FROM TinyBlog ORDER BY id
分区分布
--查看分区架构文件组分布SELECT CONVERT(VARCHAR(MAX), ps.name) AS partition_scheme , p.partition_number , CONVERT(VARCHAR(MAX), ds2.name) AS filegroup , CONVERT(VARCHAR(MAX), ISNULL(v.value, ''), 120) AS range_boundary , STR(p.rows, 9) AS rowsFROM sys.indexes i JOIN sys.partition_schemes ps ON i.data_space_id = ps.data_space_id JOIN sys.destination_data_spaces dds ON ps.data_space_id = dds.partition_scheme_id JOIN sys.data_spaces ds2 ON dds.data_space_id = ds2.data_space_id JOIN sys.partitions p ON dds.destination_id = p.partition_number AND p.object_id = i.object_id AND p.index_id = i.index_id JOIN sys.partition_functions pf ON ps.function_id = pf.function_id LEFT JOIN sys.Partition_Range_values v ON pf.function_id = v.function_id AND v.boundary_id = p.partition_number - pf.boundary_value_on_rightWHERE i.object_id = OBJECT_ID('TinyBlog') AND i.index_id IN ( 0, 1 )ORDER BY p.partition_number--分区区间--SELECT * FROM sys.partition_range_values 
分区情况
--分区情况SELECT c.* , b.[groupname] AS '分区方案对应的文件组名称' , d.name '当前分区函数对应的分区方案'FROM sys.destination_data_spaces AS a INNER JOIN sysfilegroups AS b ON a.[data_space_id] = b.[groupid] INNER JOIN ( SELECT $PARTITION.Fun_TinyBlog_Id(id) AS 分区编号 , MIN(id) AS Min_value , MAX(id) AS Max_value , COUNT(id) AS 记录数 FROM [dbo].[TinyBlog] GROUP BY $PARTITION.Fun_TinyBlog_Id(id) ) AS c ON c.[分区编号] = a.[destination_id] INNER JOIN sys.partition_schemes AS d ON a.[partition_scheme_id] = d.data_space_idORDER BY c.[分区编号]
第二个视图直接把NULL值忽略了
根据第一个视图，我们画出一个总结图
分析一下
总结
结论其实很清晰，分区列不要允许NULL，如果允许列，那么我们交换分区归档数据的时候就会有麻烦了，因为无法判断分区列是NULL值的那些数据行是老数据还是新数据
相关文章：
http://www.cnblogs.com/gaizai/archive/2010/11/05/1870071.html
https://msdn.microsoft.com/zh-cn/library/ms187802.aspx
如有不对的地方，欢迎大家拍砖o(∩_∩)o