3

我需要一个返回序列的第一个元素的 FIRST 聚合函数，我将把它与 HAVING 子句一起使用。

这是一个可以看作是我之前的问题的延续：FIRST aggregate function which I can use with HAVING 子句的问题。

事实证明，只有聚合函数才能解决我的问题，所以我尝试创建一个：

[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 struct GetFirst : IBinarySerialize {

    private string allValues;

    public void Init() {
        allValues = string.Empty;
    }

    private void incrementAndAdd(SqlInt32 value) {

        allValues += (value.Value.ToString() + ",");
    }

    public void Accumulate(SqlInt32 Value) {

        incrementAndAdd(Value);
    }

    public void Merge(GetFirst Group) {

    }

    public SqlInt32 Terminate() {
        // Put your code here
        return new SqlInt32(int.Parse(allValues.Split(',')[0]));
    }

    // This is a place-holder member field
    private SqlInt32 var1;


    public void Read(System.IO.BinaryReader r) {

        allValues = r.ReadString();
    }

    public void Write(System.IO.BinaryWriter w) {

        w.Write(this.allValues);
    }
}

这就是我使用它的方式：

DECLARE @fooTable AS TABLE(
    ID INT,
    CategoryName NVARCHAR(100),
    Name NVARCHAR(100),
    MinAllow INT,
    Price DECIMAL(18,2)
);

INSERT INTO @fooTable  VALUES(1, 'Cat1', 'Product1', 3, 112.2);
INSERT INTO @fooTable  VALUES(2, 'Cat2', 'Product2', 4, 12.34);
INSERT INTO @fooTable  VALUES(3, 'Cat1', 'Product3', 5, 233.32);
INSERT INTO @fooTable  VALUES(4, 'Cat3', 'Product4', 4, 12.43);
INSERT INTO @fooTable  VALUES(5, 'Cat3', 'Product5', 1, 13.00);
INSERT INTO @fooTable  VALUES(7, 'Cat4', 'Product7', 1, 15.00);
INSERT INTO @fooTable  VALUES(6, 'Cat4', 'Product6', 3, 13.00);

DECLARE @minAllowParam AS INT = 3;

SELECT ft.CategoryName, SUM(ft.Price), dbo.GetFirst(ft.MinAllow) FROM @fooTable ft
GROUP BY ft.CategoryName
HAVING dbo.GetFirst(ft.MinAllow) >= @minAllowParam;

它有时会返回正确的结果，有时不会，我不确定我是否正确实施了它。考虑到我的要求，如果我做对了，有什么想法吗？

4

1 回答 1

3

我认为您的问题是IsInvariantToOrder尚未实现。

保留供将来使用。查询处理器当前未使用此属性：当前无法保证顺序。

所以不能保证你的函数会以正确的顺序被调用，甚至在运行之间也不能保证相同的顺序。

我不太了解 C#，但我认为你的函数可以有两个参数，第二个是你想要排序的字段。将这些对保存在列表中并在返回第一个值之前对第二个字段进行排序。

更新：

我不使用 C#，因此这里可能存在许多我看不到的错误错误做法。但看起来它在我所做的测试中工作得很好。

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 GetFirst : IBinarySerialize
{
    private int Value;
    private int OrderBy;

[SqlFunctionAttribute(IsDeterministic = true)]
    public void Init()
    {
      Value = 0;
      OrderBy = int.MaxValue;
    }

[SqlFunctionAttribute(IsDeterministic = true)]
    public void Accumulate(SqlInt32 SValue, SqlInt32 SOrderBy)
    {
        if (SValue.IsNull)
        {
            return;
        }

        if (SOrderBy.IsNull)
        {
            return;
        }

        if (SOrderBy.Value < OrderBy)
        {
            Value = SValue.Value;
            OrderBy = SOrderBy.Value;
        }
    }

[SqlFunctionAttribute(IsDeterministic = true)]
    public void Merge(GetFirst other)
    {
        if (other.OrderBy < OrderBy)
        {
            Value = other.Value;
            OrderBy = other.OrderBy;
        }
    }

[SqlFunctionAttribute(IsDeterministic = true)]
    public SqlInt32 Terminate()
    {
      return new SqlInt32(Value);
    }

[SqlFunctionAttribute(IsDeterministic = true)]
    public void Read(BinaryReader r)
    {
        Value = r.ReadInt32();
        OrderBy = r.ReadInt32();
    }

[SqlFunctionAttribute(IsDeterministic = true)]
    public void Write(BinaryWriter w)
    {
        w.Write(Value);
        w.Write(OrderBy);
    }
}

安装：

CREATE ASSEMBLY GetFirstAsm FROM 'First.dll'
GO
CREATE AGGREGATE GetFirst (@Value int, @OrderBy int) RETURNS int
EXTERNAL NAME GetFirstAsm.GetFirst

像这样使用：

declare @T table
(
  ID1 int,
  ID2 int,
  Val int,
  Grp int
)

insert into @T values
(1, 5, '1', 1),
(2, 4, '2', 1),
(3, 3, '3', 1),
(4, 2, '4', 2),
(5, 1, '5', 2)

select Grp, dbo.GetFirst(Val, ID1) as Val
from @T
group by Grp

select Grp, dbo.GetFirst(Val, ID2) as Val
from @T
group by Grp

结果：

(5 row(s) affected)
Grp         Val
----------- -----------
1           1
2           4

(2 row(s) affected)

Grp         Val
----------- -----------
1           3
2           5

(2 row(s) affected)
于 2012-04-12T11:44:31.157 回答