具有多个参数的 SQLCLR 自定义聚合 [英] SQLCLR custom aggregate with multiple parameters

问题描述

我无法理解 CLR 用户定义聚合的工作原理.

I have trouble understanding of how CLR User-Defined Aggregates work.

我必须创建一些具有多个参数的自定义 CLR 聚合.重点是根据第二个参数获取第一个参数的值.

I have to create some custom CLR aggregates with multiple parameters. The point is to get the value of the first parameter depending on the second.

例如，我的表中有以下值，我需要每个 Type 的最老员工 Name:

For example, I have the following values in my table, and I need the oldest employee Name for each Type:

    Type   |   Name   |   Age   
--------------------------------
Manager    | emp 1    |   35    
Manager    | emp 2    |   42    
Developer  | emp 3    |   36    
Developer  | emp 4    |   45    
Developer  | emp 5    |   22    

所以我想写一个这样的查询来使用我的程序集获取结果:

So I would like to write a query like this to get the result by using my assembly:

Select      Type, dbo.fOldestEmployee(Name, Age) AS [Name]
From        xxx
Group By    Type

这将响应:

    Type   |   Name   
----------------------
Manager    | emp 2     
Developer  | emp 4    

看起来使用 CLR 用户定义的聚合是可能的，但我很难找到这种实现的具体示例.

It look like it's possible with a CLR User-Defined Aggregate, but I have difficulty finding a concrete example of this kind of implementation.

目前我有这个.我创建了一个类来收集数据，但我如何对它们进行排序(或做其他事情)?

For the moment I have this. I create a class to collect the datas, but how can I sort (or do other thing) to them?

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

[Serializable]
[SqlUserDefinedAggregate(
    Format.UserDefined,
    IsInvariantToOrder = false, // order changes the result
    IsInvariantToNulls = false, // nulls change the result
    IsInvariantToDuplicates = false, // duplicates change the result
    MaxByteSize = -1)]
public struct sOlder
{
    private List<MyData> _datas;

    public void Init()
    {
        _datas = new List<MyData>();
    }

    public void Accumulate(SqlString valueField, SqlInt32 ValueInt)
    {
        if (!valueField.IsNull && !ValueInt.IsNull)
        {
            _datas.Add(new MyData
            {
                ValField = valueField.Value,
                ValInt = ValueInt.Value
            });
        }
    }

    public void Merge (sOlder Group)
    {
        _datas.AddRange(Group._datas);
    }

    public SqlString Terminate ()
    {
        //...
    }

    public class MyData
    {
        public String ValField { get; set; }
        public Int32 ValInt { get; set; }
    }
}

有什么想法吗?

推荐答案

无需存储所有记录的列表 - 您只需要存储迄今为止看到的最旧记录的详细信息.

There's no need to store a list of all the records - you only need to store the details of the oldest record you've seen so far.

这样的事情应该可以工作:

Something like this should work:

[Serializable]
[SqlUserDefinedAggregate(
    Format.UserDefined,
    IsInvariantToOrder = true,
    IsInvariantToNulls = true,
    IsInvariantToDuplicates = true,
    MaxByteSize = -1)]
public struct sOlder : IBinarySerialize
{
    private struct MyData
    {
        public string Name { get; set; }
        public int? Age { get; set; }

        public int CompareTo(MyData other)
        {
            if (Age == null) return other.Age == null ? 0 : -1;
            if (other.Age == null) return 1;
            return Age.Value.CompareTo(other.Age.Value);
        }

        public static bool operator <(MyData left, MyData right)
        {
            return left.CompareTo(right) == -1;
        }

        public static bool operator >(MyData left, MyData right)
        {
            return left.CompareTo(right) == 1;
        }
    }

    private MyData _eldestPerson;

    public void Init()
    {
        _eldestPerson = default(MyData);
    }

    public void Accumulate(SqlString name, SqlInt32 age)
    {
        if (!name.IsNull && !age.IsNull)
        {
            var currentPerson = new MyData
            {
                Name = name.Value,
                Age = age.Value
            };

            if (currentPerson > _eldestPerson)
            {
                _eldestPerson = currentPerson;
            }
        }
    }

    public void Merge (sOlder other)
    {
        if (other._eldestPerson > _eldestPerson)
        {
            _eldestPerson = other._eldestPerson;
        }
    }

    public SqlString Terminate()
    {
        return _eldestPerson.Name;
    }

    public void Write(BinaryWriter writer)
    {
        if (_eldestPerson.Age.HasValue)
        {
            writer.Write(true);
            writer.Write(_eldestPerson.Age.Value);
            writer.Write(_eldestPerson.Name);
        }
        else
        {
            writer.Write(false);
        }
    }

    public void Read(BinaryReader reader)
    {
        if (reader.ReadBoolean())
        {
            _eldestPerson.Age = reader.ReadInt32();
            _eldestPerson.Name = reader.ReadString();
        }
        else
        {
            _eldestPerson = default(MyData);
        }
    }
}

这篇关于具有多个参数的 SQLCLR 自定义聚合的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！