此类问题还可以延伸到类似进销存的批次计算中，这也要关注其他历史记录来决定当前某条记录的状态。
sql语句无法简单实现mdx语句的类似功能，必须得用交叉表关联来对比。这里我们用CLR函数来实现mdx语句的类似语法。在select的时候把得到过的做个缓存就可以了。效率应该可以提高不少。
clr的代码如下，编译为TestFun.dll，复制到sql服务器的文件目录下。
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复制代码 代码如下:
using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
public partial class UserDefinedFunctions
{
// 保存当前组当前值
private static System.Collections.Generic.Dictionary <string , SqlString > _listValue = new System.Collections.Generic.Dictionary <string , SqlString >();
// 保存当前组
private static System.Collections.Generic.Dictionary <string , string > _listGroup = new System.Collections.Generic.Dictionary <string , string >();
/// <summary>
/// 获取当前组上条记录数值
/// </summary>
/// <param name="key"> 并发键 </param>
/// <param name="currentGroup"> 当前组 </param>
/// <param name="currentValue"> 当前组当前值 </param>
/// <returns></returns>
[Microsoft.SqlServer.Server.SqlFunction ]
public static SqlString GetPrevMemberValue(SqlString key,SqlString currentGroup,SqlString currentValue)
{
if (key.IsNull || currentGroup.IsNull) return SqlString .Null;
try
{
SqlString prevMemberValue = _listValue[key.Value];
// 组变更
if (_listGroup[key.Value] != currentGroup.Value)
{
prevMemberValue = SqlString .Null;
_listGroup[key.Value] = currentGroup.Value;
}
// 值变更
_listValue[key.Value] = currentValue;
return prevMemberValue;
}
catch
{
return SqlString .Null;
}
}
/// <summary>
/// 初始化并发键
/// </summary>
/// <param name="key"></param>
/// <returns></returns>
[Microsoft.SqlServer.Server.SqlFunction ]
public static SqlBoolean InitKey(SqlString key)
{
try
{
_listValue.Add(key.Value, SqlString .Null);
_listGroup.Add(key.Value, string .Empty);
return true ;
}
catch
{
return false ;
}
}
/// <summary>
/// 释放并发键
/// </summary>
/// <param name="key"></param>
/// <returns></returns>
[Microsoft.SqlServer.Server.SqlFunction ]
public static SqlBoolean DisposeKey(SqlString key)
{
try
{
_listValue.Remove(key.Value);
_listGroup.Remove(key.Value);
return true ;
}
catch
{
return false ;
}
}
};
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部署和生成自定义函数，其中考虑到并发，我们还是需要一个并发键来表达当前查询
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复制代码 代码如下:
CREATE ASSEMBLY TestForSQLCLR FROM 'E:/sqlclrdata/TestFun.dll' WITH PERMISSION_SET = UnSAFE;
--
go
CREATE FUNCTION dbo. xfn_GetPrevMemberValue
(
@key nvarchar ( 255),
@initByDim nvarchar ( 255),
@currentValue nvarchar ( 255)
)
RETURNS nvarchar ( 255)
AS EXTERNAL NAME TestForSQLCLR. [UserDefinedFunctions]. GetPrevMemberValue
go
CREATE FUNCTION dbo. xfn_initKey
(
@key nvarchar ( 255)
)
RETURNS bit
AS EXTERNAL NAME TestForSQLCLR. [UserDefinedFunctions]. InitKey
go
CREATE FUNCTION dbo. xfn_disposeKey
(
@key nvarchar ( 255)
)
RETURNS bit
AS EXTERNAL NAME TestForSQLCLR. [UserDefinedFunctions]. DisposeKey
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这样我们就可以使用了，测试脚本如下， xfn_GetPrevMemberValue就是获取上月价格的函数。
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-- 建立测试环境
复制代码 代码如下:
declare @t table (
[ 区域 ] [varchar]( 4) COLLATE Chinese_PRC_CI_AS NULL,
[TradeMonth] [varchar]( 7) COLLATE Chinese_PRC_CI_AS NULL,
[TradeMoney] [float] NULL,
[TradeArea] [float] NULL,
[TradePrice] [float] NULL
)
insert into @t
select ' 闵行 ' , '2007-03' , '2125714.91' , '241.65' , '8796.67' union
select ' 闵行 ' , '2007-04' , '8408307.64' , '907.32' , '9267.19' union
select ' 闵行 ' , '2007-05' , '10230321.95' , '1095.88' , '9335.26' union
select ' 浦东 ' , '2007-01' , '12738432.25' , '1419.05' , '8976.73' union
select ' 浦东 ' , '2007-02' , '4970536.74' , '395.49' , '12568.05' union
select ' 浦东 ' , '2007-03' , '5985405.76' , '745.94' , '8023.98' union
select ' 浦东 ' , '2007-04' , '21030788.61' , '1146.89' , '18337.23' union
select ' 普陀 ' , '2007-01' , '1863896' , '161.39' , '11549.02' union
select ' 普陀 ' , '2007-02' , '1614015' , '119.59' , '13496.24' union
select ' 普陀 ' , '2007-03' , '1059235.19' , '135.21' , '7834'
-- 测试语句
复制代码 代码如下:
declare @key varchar ( 40)
declare @b bit
set @key= newid ()
select @b= dbo. xfn_initKey( @key)
select 区域 , TradeMonth, TradePrice, LastMonthPrice,
cast ( round (( Tradeprice- LastMonthPrice)* 100/ LastMonthPrice, 2) as varchar ( 10))+ '%' as 环比 from (
select *, cast ( dbo. xfn_GetPrevMemberValue( @key, 区域 , Tradeprice) as float ) as LastMonthPrice from @t
) t
select @b= dbo. xfn_disposeKey( @key)
-- 结果
/*
区域 TradeMonth TradePrice LastMonthPrice 环比
---- ---------- ---------------------- ---------------------- -----------
闵行 2007-03 8796.67 NULL NULL
闵行 2007-04 9267.19 8796.67 5.35%
闵行 2007-05 9335.26 9267.19 0.73%
浦东 2007-01 8976.73 NULL NULL
浦东 2007-02 12568.05 8976.73 40.01%
浦东 2007-03 8023.98 12568 -36.16%
浦东 2007-04 18337.23 8023.98 128.53%
普陀 2007-01 11549.02 NULL NULL
普陀 2007-02 13496.24 11549 16.86%
普陀 2007-03 7834 13496.2 -41.95%
*/
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这个函数写的还是比较粗糙，如果进一步改进还可以详细定义如何获取上一个维度的方法。这里只是根据查询顺序来做缓存。感兴趣的朋友可以完善一下。