自定义sql server 聚合涵数

using System;

using System.Data;

using System.Data.SqlClient;

using System.Data.SqlTypes;

using Microsoft.SqlServer.Server;

using System.Text;

using System.Collections.Generic;

[Serializable]

[Microsoft.SqlServer.Server.SqlUserDefinedAggregate(Format.UserDefined,

    IsInvariantToDuplicates = false,

    IsInvariantToNulls = true,

    IsInvariantToOrder = false,

    IsNullIfEmpty = true,

    MaxByteSize = 8000

)]

public struct SumPart : IBinarySerialize

{

    private StringBuilder _reuslt;

    //private List<string> _li ;

    public void Init()

    {

        // 在此处放置代码

        _reuslt = new StringBuilder();

        //_li = new List<string>();

    }

    public void Accumulate(SqlString Value)

    {

        // 在此处放置代码

        if (Value.IsNull)

        {

            return;

        }

        else

        {

            //_li.Add(Value.Value);

            if (_reuslt.Length > 0)

            {

                _reuslt.Append("$");

            }

            _reuslt.Append(Value.Value);

        }

    }

    public void Merge(SumPart Group)

    {

        // 在此处放置代码

        _reuslt.Append(Group._reuslt);

    }

    public SqlString Terminate()

    {

        // 在此处放置代码

        //if(li.Count>0)  为什么li老是==null???? 

        //if (_li == null)

        //{

        //    return new SqlString("");

        //}

        if (_reuslt.Length > 0)

        {

            string strReturn = "";

            string[] arrayStr = _reuslt.ToString().Split('$');

            List<string> li = new List<string>();

            for (int i = 0; i < arrayStr.Length; i++)

            {

                li.Add(arrayStr[i]);

            }

            li.Sort();

            foreach (string item in li)

            {

                strReturn += "$"+item ;

            }

            return new SqlString(strReturn);

            //return new SqlString(_reuslt.ToString());

        }

        return new SqlString("");

    }

    // 这是占位符成员字段

    private int var1;

    #region IBinarySerialize 成员

    public void Read(System.IO.BinaryReader r)

    {

        _reuslt = new StringBuilder(r.ReadString());

    }

    public void Write(System.IO.BinaryWriter w)

    {

        w.Write(_reuslt.ToString());

    }

    #endregion

}