CLR 使用者定義匯總 - 叫用函式

發行項
07/04/2024

適用於：SQL Server

在 Transact-SQL SELECT 語句中，您可以叫用 Common Language Runtime （CLR）使用者定義匯總，受限於套用至系統聚合函數的所有規則。

下列其他規則適用：

目前用戶必須具有 使用者定義匯總的 EXECUTE 許可權。
使用者定義匯總必須使用schema_name.udagg_name 格式的兩部分名稱來叫用。
使用者定義匯總的自變數類型必須符合或隱含轉換成匯總的input_type，如 CREATE AGGREGATE 語句中所定義。
使用者定義匯總的傳回型別必須符合 CREATE AGGREGATE 語句中的return_type。

範例 1

以下是使用者定義聚合函數的範例，會串連一組從數據表中的數據行擷取的字串值：

[C#]

using System;  
using System.Data;  
using Microsoft.SqlServer.Server;  
using System.Data.SqlTypes;  
using System.IO;  
using System.Text;  
  
[Serializable]  
[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 Concatenate : IBinarySerialize  
{  
    /// <summary>  
    /// The variable that holds the intermediate result of the concatenation  
    /// </summary>  
    public StringBuilder intermediateResult;  
  
    /// <summary>  
    /// Initialize the internal data structures  
    /// </summary>  
    public void Init()  
    {  
        this.intermediateResult = new StringBuilder();  
    }  
  
    /// <summary>  
    /// Accumulate the next value, not if the value is null  
    /// </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="other"></param>  
    public void Merge(Concatenate other)  
    {  
        this.intermediateResult.Append(other.intermediateResult);  
    }  
  
    /// <summary>  
    /// Called at the end of aggregation, to return the results of the aggregation.  
    /// </summary>  
    /// <returns></returns>  
    public SqlString Terminate()  
    {  
        string output = string.Empty;  
        //delete the trailing comma, if any  
        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());  
    }  
}

[Visual Basic]

Imports System  
Imports System.Data  
Imports Microsoft.SqlServer.Server  
Imports System.Data.SqlTypes  
Imports System.IO  
Imports System.Text  
  
<Serializable(), SqlUserDefinedAggregate(Format.UserDefined, IsInvariantToNulls:=True, IsInvariantToDuplicates:=False, IsInvariantToOrder:=False, MaxByteSize:=8000)> _  
Public Class Concatenate  
    Implements IBinarySerialize  
  
    ''' <summary>  
    ''' The variable that holds the intermediate result of the concatenation  
    ''' </summary>  
    Public intermediateResult As StringBuilder  
  
    ''' <summary>  
    ''' Initialize the internal data structures  
    ''' </summary>  
    Public Sub Init()  
        Me.intermediateResult = New StringBuilder()  
    End Sub  
  
    ''' <summary>  
    ''' Accumulate the next value, not if the value is null  
    ''' </summary>  
    ''' <param name="value"></param>  
    Public Sub Accumulate(ByVal value As SqlString)  
        If value.IsNull Then  
            Return  
        End If  
  
        Me.intermediateResult.Append(value.Value).Append(","c)  
    End Sub  
    ''' <summary>  
    ''' Merge the partially computed aggregate with this aggregate.  
    ''' </summary>  
    ''' <param name="other"></param>  
    Public Sub Merge(ByVal other As Concatenate)  
        Me.intermediateResult.Append(other.intermediateResult)  
    End Sub  
  
    ''' <summary>  
    ''' Called at the end of aggregation, to return the results of the aggregation.  
    ''' </summary>  
    ''' <returns></returns>  
    Public Function Terminate() As SqlString  
        Dim output As String = String.Empty  
  
        'delete the trailing comma, if any  
        If Not (Me.intermediateResult Is Nothing) AndAlso Me.intermediateResult.Length > 0 Then  
            output = Me.intermediateResult.ToString(0, Me.intermediateResult.Length - 1)  
        End If  
  
        Return New SqlString(output)  
    End Function  
  
    Public Sub Read(ByVal r As BinaryReader) Implements IBinarySerialize.Read  
        intermediateResult = New StringBuilder(r.ReadString())  
    End Sub  
  
    Public Sub Write(ByVal w As BinaryWriter) Implements IBinarySerialize.Write  
        w.Write(Me.intermediateResult.ToString())  
    End Sub  
End Class

將程式代碼編譯成 MyAgg.dll之後，您可以在 SQL Server 中註冊匯總，如下所示：

CREATE ASSEMBLY MyAgg FROM 'C:\MyAgg.dll';  
GO  
CREATE AGGREGATE MyAgg (@input nvarchar(200)) RETURNS nvarchar(max)  
EXTERNAL NAME MyAgg.Concatenate;

注意

C++ SQL Server 中不支援使用 /clr：pure 編譯選項編譯的資料庫物件，例如純量值函式等資料庫物件。

和大部分匯總一樣，大部分的邏輯都位於 Aggregate 方法中。在這裡，當做參數傳遞至 Accumulate 方法的字串會附加至 Init 方法中初始化的 StringBuilder 物件。假設這不是第一次 呼叫 Accumulate 方法，在附加傳入字串之前，也會將逗號附加至 StringBuilder 。在計算工作結束時， 會呼叫 Terminate 方法，以字串的形式傳 回 StringBuilder 。

例如，請考慮具有下列架構的數據表：

CREATE TABLE BookAuthors  
(  
   BookID   int       NOT NULL,  
   AuthorName    nvarchar(200) NOT NULL  
);

然後插入下列資料欄位：

INSERT BookAuthors VALUES(1, 'Johnson'),(2, 'Taylor'),(3, 'Steven'),(2, 'Mayler'),(3, 'Roberts'),(3, 'Michaels');

然後，下列查詢會產生下列結果：

SELECT BookID, dbo.MyAgg(AuthorName)  
FROM BookAuthors  
GROUP BY BookID;

BookID	作者名稱
1	約翰生
2	泰勒，梅勒
3	羅伯茨、邁克爾斯、史蒂文

範例 2

下列範例顯示 Aggregate 方法上有兩個參數的匯總。

[C#]

using System;  
using System.Data;  
using System.Data.SqlClient;  
using System.Data.SqlTypes;  
using Microsoft.SqlServer.Server;  
  
[Serializable]  
[SqlUserDefinedAggregate(  
    Format.Native,  
    IsInvariantToDuplicates = false,  
    IsInvariantToNulls = true,  
    IsInvariantToOrder = true,  
    IsNullIfEmpty = true,  
    Name = "WeightedAvg")]  
public struct WeightedAvg  
{  
    /// <summary>  
    /// The variable that holds the intermediate sum of all values multiplied by their weight  
    /// </summary>  
    private long sum;  
  
    /// <summary>  
    /// The variable that holds the intermediate sum of all weights  
    /// </summary>  
    private int count;  
  
    /// <summary>  
    /// Initialize the internal data structures  
    /// </summary>  
    public void Init()  
    {  
        sum = 0;  
        count = 0;  
    }  
  
    /// <summary>  
    /// Accumulate the next value, not if the value is null  
    /// </summary>  
    /// <param name="Value">Next value to be aggregated</param>  
    /// <param name="Weight">The weight of the value passed to Value parameter</param>  
    public void Accumulate(SqlInt32 Value, SqlInt32 Weight)  
    {  
        if (!Value.IsNull && !Weight.IsNull)  
        {  
            sum += (long)Value * (long)Weight;  
            count += (int)Weight;  
        }  
    }  
  
    /// <summary>  
    /// Merge the partially computed aggregate with this aggregate  
    /// </summary>  
    /// <param name="Group">The other partial results to be merged</param>  
    public void Merge(WeightedAvg Group)  
    {  
        sum += Group.sum;  
        count += Group.count;  
    }  
  
    /// <summary>  
    /// Called at the end of aggregation, to return the results of the aggregation.  
    /// </summary>  
    /// <returns>The weighted average of all inputed values</returns>  
    public SqlInt32 Terminate()  
    {  
        if (count > 0)  
        {  
            int value = (int)(sum / count);  
            return new SqlInt32(value);  
        }  
        else  
        {  
            return SqlInt32.Null;  
        }  
    }  
}

[Visual Basic]

Imports System  
Imports System.Data  
Imports System.Data.SqlClient  
Imports System.Data.SqlTypes  
Imports Microsoft.SqlServer.Server  
Imports System.Runtime.InteropServices  
  
<StructLayout(LayoutKind.Sequential)> _  
<Serializable(), SqlUserDefinedAggregate(Format.Native, _  
IsInvariantToDuplicates:=False, _  
IsInvariantToNulls:=True, _  
IsInvariantToOrder:=True, _  
IsNullIfEmpty:=True, _  
Name:="WeightedAvg")> _  
Public Class WeightedAvg  
  
    ''' <summary>  
    ''' The variable that holds the intermediate sum of all values multiplied by their weight  
    ''' </summary>  
    Private sum As Long  
  
    ''' <summary>  
    ''' The variable that holds the intermediate sum of all weights  
    ''' </summary>  
    Private count As Integer  
  
    ''' <summary>  
    ''' The variable that holds the intermediate sum of all weights  
    ''' </summary>  
    Public Sub Init()  
        sum = 0  
        count = 0  
    End Sub  
  
    ''' <summary>  
    ''' Accumulate the next value, not if the value is null  
    ''' </summary>  
    ''' <param name="Value">Next value to be aggregated</param>  
    ''' <param name="Weight">The weight of the value passed to Value parameter</param>  
    Public Sub Accumulate(ByVal Value As SqlInt32, ByVal Weight As SqlInt32)  
        If Not Value.IsNull AndAlso Not Weight.IsNull Then  
            sum += CType(Value, Long) * CType(Weight, Long)  
            count += CType(Weight, Integer)  
        End If  
    End Sub  
  
    ''' <summary>  
    ''' Merge the partially computed aggregate with this aggregate.  
    ''' </summary>  
    ''' <param name="Group">The other partial results to be merged</param>  
    Public Sub Merge(ByVal Group As WeightedAvg)  
        sum = Group.sum  
        count = Group.count  
    End Sub  
  
    ''' <summary>  
    ''' Called at the end of aggregation, to return the results of the aggregation.  
    ''' </summary>  
    ''' <returns>The weighted average of all inputed values</returns>  
    Public Function Terminate() As SqlInt32  
        If count > 0 Then  
            ''                        int value = (int)(sum / count);  
            ''          return new SqlInt32(value);  
            Dim value As Integer = CType(sum / count, Integer)  
            Return New SqlInt32(value)  
        Else  
            Return SqlInt32.Null  
        End If  
    End Function  
End Class

編譯 C# 或 Visual Basic 原始程式碼之後，請執行下列 Transact-SQL。此腳本假設 DLL 稱為 WghtAvg.dll，且位於 C 磁碟驅動器的根目錄中。也會假設名為test的資料庫。

use test;  
go  
  
-- sp_configure 'clr enabled', 1;  
-- go  
  
--- RECONFIGURE WITH OVERRIDE;  
-- go  
  
IF EXISTS (SELECT name FROM systypes WHERE name = 'MyTableType')  
   DROP TYPE MyTableType;  
go  
  
IF EXISTS (SELECT name FROM sysobjects WHERE name = 'WeightedAvg')  
   DROP AGGREGATE WeightedAvg;  
go  
  
IF EXISTS (SELECT name FROM sys.assemblies WHERE name = 'MyClrCode')  
   DROP ASSEMBLY MyClrCode;  
go  
  
CREATE ASSEMBLY MyClrCode FROM 'C:\WghtAvg.dll';  
GO  
  
CREATE AGGREGATE WeightedAvg (@value int, @weight int) RETURNS int  
EXTERNAL NAME MyClrCode.WeightedAvg;  
go  
  
CREATE TYPE MyTableType AS table (ItemValue int, ItemWeight int);  
go  
  
DECLARE @myTable AS MyTableType;  
  
INSERT INTO @myTable VALUES(1, 4), (6, 1);  
  
SELECT dbo.WeightedAvg(ItemValue, ItemWeight) FROM @myTable;  
go

另請參閱

CLR 使用者定義匯總

共用方式為

CLR 使用者定義匯總 - 叫用函式

範例 1

範例 2

另請參閱

意見反應

其他資源