是否可以将用户定义的聚合(clr)与窗口函数(over)一起使用? [英] Is it possible to use user defined aggregates (clr) with window functions (over)?

问题描述

是否可以将用户定义的聚合(clr)与窗口函数(over)一起使用?

Is it possible to use user defined aggregates (clr) with window functions (over) ?

在文档中找不到答案:http://technet.microsoft.com/en-us/library/ms190678.aspx

推荐答案

您说得对，在文档中查找任何内容都很棘手.但是搜索 Connect 网站，我设法找到了这个 gem:

You're right that it's tricky to find anything in the documentation. But searching the Connect website, I managed to find this gem:

今天，您可以像常规聚合函数一样使用带有 OVER 子句和 PARTITION BY 的 CLR 聚合.一旦我们支持窗口函数...

Today, you can use CLR aggregates with OVER clause and PARTITION BY just like regular aggregate functions. Once we have support for window functions...

这是微软的回应.

但是，在我等待旧机器创建新数据库项目并创建此聚合时，我在 Connect 站点上进行了搜索:

However, searching on the Connect site was what I did whilst I was waiting for my aged machine to create a new database project and create this aggregate:

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using System.IO;
using Microsoft.SqlServer.Server;

[Serializable]
[Microsoft.SqlServer.Server.SqlUserDefinedAggregate(Format.UserDefined,MaxByteSize = 2000)]
public struct SqlAggregate1 : IBinarySerialize
{
    private SqlString last;
    public void Init()
    {
        // Ignore
    }

    public void Accumulate(SqlString Value)
    {
        last = Value;
    }

    public void Merge (SqlAggregate1 Group)
    {
        // Ignore
    }

    public SqlString Terminate ()
    {
        // Put your code here
        return last;
    }

    public void Read(BinaryReader r)
    {
        last = new SqlString(r.ReadString());
    }

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

然后运行这个脚本:

select dbo.SqlAggregate1(Column2) OVER (PARTITION BY Column1)
from (select 1,'abc' union all select 1,'def' union all
      select 2,'ghi' union all select 2,'jkl') as t(Column1,Column2)

产生:

------------
abc
abc
ghi
ghi

说起来还很长——只要尝试，您就可以很容易地为自己找到答案.

Which is a long way to say - you could have easily discovered the answer for yourself just by trying it.

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