说明:本文依据网络转载整理而成,因为时间关系,其中原理暂时并未深入研究,只是整理备份留个记录而已。
目标:在SQL Server中自定义聚合函数,在Group BY语句中 ,不是单纯的SUM和MAX等运算,可以加入拼接字符串。
环境:
1:Sqlserver 2008 R2
2:Visual Studio 2013
第一部分:
.net代码:
using System; using System.Data; using Microsoft.SqlServer.Server; using System.Data.SqlTypes; using System.IO; using System.Text; [Serializable] [SqlUserDefinedAggregate( Format.UserDefined, //使用UserDefined 序列化格式 IsInvariantToNulls = true, //聚合是否与空值有关 IsInvariantToDuplicates = false, //聚合是否与重复值有关 IsInvariantToOrder = false, //聚合是否与顺序有关 MaxByteSize = 8000) //聚合实例的最大大小(以字节为单位) ] public class Concatenate : IBinarySerialize { /// <summary> /// 定义变量 /// </summary> private StringBuilder intermediateResult; /// <summary> /// 初始化 /// </summary> public void Init() { this.intermediateResult = new StringBuilder(); } /// <summary> /// 如果某一个字符不为空,用";"追加 /// </summary> /// <param name="value"></param> public void Accumulate(SqlString value,string contChar) //symbol { if (value.IsNull) { return; } this.intermediateResult.Append(value.Value).Append(contChar); } /// <summary> /// 合并字符 /// </summary> /// <param name="other"></param> public void Merge(Concatenate other) { this.intermediateResult.Append(other.intermediateResult); } /// <summary> /// 处理最后的"," /// </summary> /// <returns></returns> public SqlString Terminate() { string output = string.Empty; //删除最后的"," if (this.intermediateResult != null && this.intermediateResult.Length > 0) { output = this.intermediateResult.ToString(0, this.intermediateResult.Length - 1); } return new SqlString(output); } public void Read(BinaryReader r) { intermediateResult = new StringBuilder(r.ReadString()); } public void Write(BinaryWriter w) { w.Write(this.intermediateResult.ToString()); } }
编译生成DLL,注意:SqlServer 2008 R2 不支持.Net Framework 4.5 ,所以生成dll的时候选在.net framework 3.5
第二步:启用数据库对CLR支持的配置
EXEC sp_configure ‘clr enabled‘, 1 RECONFIGURE WITH OVERRIDE GO
第三步:加载CLR程序集并创建自定义函数
USE Test --选择数据库 CREATE ASSEMBLY SQL_Aggregate FROM ‘E:\WorkSpace\LetMeTry\WindowsFormsApplication2\SqlCustomFunction\bin\Debug\SqlCustomFunction.dll‘ --生成的DLL路径 GO CREATE AGGREGATE SQL_Aggregate (@input nvarchar(200),@contChar nvarchar(1)) RETURNS nvarchar(max) EXTERNAL NAME SQL_Aggregate.Concatenate
第四步:测试
USE Test --创建测试数据 create table tb(ID int,Name varchar(10)) insert into tb select 1,‘a‘ union all select 1,‘b‘ union all select 2,‘c‘ union all select 2,‘e‘ union all select 3,‘d‘ go --自定义聚合函数使用例子(第二个参数为拼接字符串的连接符) select id,dbo.SQL_Aggregate([Name],‘+‘) AS Test from tb group by id
时间: 2024-11-06 20:01:29