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 resultIsInvariantToNulls = true, //optimizer propertyIsInvariantToDuplicates = false, //optimizer propertyIsInvariantToOrder = false, //optimizer propertyMaxByteSize = 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());}
}

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];

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