SQL2005CLR函数扩展-深入环比计算的详解

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 ;
        }
    }
};

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

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'

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)