sql server 2012 自定义聚合函数(MAX_O3_8HOUR_ND) 计算最大的臭氧8小时滑动平均值

采用c#开发dll，并添加到sql server 中。

具体代码，可以用visual studio的向导生成模板。

using System;
using System.Collections;
using System.Data;
using Microsoft.SqlServer.Server;
using System.Data.SqlTypes;
using System.IO;
using System.Text;

[Serializable]
[Microsoft.SqlServer.Server.SqlUserDefinedAggregate(
    Format.UserDefined, //use clr serialization to serialize the intermediate result
    IsInvariantToNulls = true, //optimizer property
    IsInvariantToDuplicates = false, //optimizer property
    IsInvariantToOrder = false, //optimizer property
    MaxByteSize = 8000) //maximum size in bytes of persisted value
]
public class MAX_O3_8HOUR_ND : IBinarySerialize
{
    /// <summary>
    /// The variable that holds the intermediate result of the concatenation
    /// </summary>
    private StringBuilder intermediateResult;

    /// <summary>
    /// 系统初始化
    /// </summary>
    public void Init()
    {
        this.intermediateResult = new StringBuilder();
    }

    /// <summary>
    /// 积累文本内容，null除外，一般用标点符号隔开。
    /// </summary>
    /// <param name="value"></param>
    public void Accumulate(SqlString value)
    {
        if (value.IsNull)
        {
            return;
        }

        this.intermediateResult.Append(value.Value).Append(',');
    }

    /// <summary>
    /// Merge the partially computed aggregate with this aggregate.
    /// </summary>
    /// <param name="Group"></param>
    public void Merge(MAX_O3_8HOUR_ND Group)
    {
        this.intermediateResult.Append(Group.intermediateResult);
    }

    /// <summary>
    ///在最后被调用，返回聚合函数结果
    /// </summary>
    /// <returns></returns>
    public SqlString Terminate()
    {
        string output = string.Empty;
        ArrayList list = new ArrayList();
        if (this.intermediateResult != null&& this.intermediateResult.Length > 0)
        {
            output = this.intermediateResult.ToString(0, this.intermediateResult.Length - 1);
            string [] result=output.Split(',');
            float max = 0;
            if (result.Length >= 8)
            {
                for (int i = 0; i <= result.Length - 8; i++)
                {
                    float re = 0;
                    for (int j = i; j < 8 + i; j++)
                    {
                        re = re + Convert.ToSingle(result[j]);
                    }
                    re=re/8;
                    if (re > max)
                    {
                        max = re;
                    }
                }
                output = Math.Ceiling(max).ToString();
            }
            else
            {
                output=string.Empty;
            }

        }

        return new SqlString(output);
    }

    public void Read(BinaryReader r)
    {
        intermediateResult = new StringBuilder(r.ReadString());
    }

    public void Write(BinaryWriter w)
    {
        w.Write(this.intermediateResult.ToString());
    }
}

dll添加到sql server，创建聚合函数。

CREATE ASSEMBLY [MAX_O3_8HOUR_ND] AUTHORIZATION [dbo]
FROM 'c:MAX_O3_8HOUR_ND.dll'
WITH PERMISSION_SET = SAFE;

CREATE AGGREGATE [dbo].[MAX_O3_8HOUR_ND] (@FieldValue [nvarchar](4000))
RETURNS [nvarchar](4000)
EXTERNAL NAME [MAX_O3_8HOUR_ND].[MAX_O3_8HOUR_ND];

sql server 开启 CLR支持：

EXEC sp_configure 'clr enabled', 1
RECONFIGURE WITH OVERRIDE
GO

示例：

SELECT FDATE,SITENAME, dbo.MAX_O3_8HOUR_ND(O3)
FROM (select top 100 percent * from MONITOR_ND order by ftime)a
GROUP BY SITENAME,FDATE