Truy vấn SQL cho các kết hợp mà không lặp lại

Tôi cần một truy vấn có thể được sử dụng trong (hoặc dưới dạng) một hàm và truy xuất tất cả các kết hợp của n giá trị. Và tôi cần tất cả các kết hợp độ dài k trong đó k = 1..n.

Đầu vào và kết quả mẫu mở rộng để đầu vào có 3 giá trị thay vì 2 - tuy nhiên, số lượng giá trị đầu vào có thể thay đổi từ 1 đến n.

Ví dụ: Input: bảng với các giá trị trong một cột trong nhiều hàng

Value  (nvarchar(500))
------
Ann
John
Mark

Đầu ra # 1: bảng với các giá trị được nối trong một cột

    Ann
    John
    Mark
    Ann,John
    John,Mark
    Ann,Mark
    Ann,John,Mark

sql-server query-performance

— tiền mã hóa
nguồn

Đối với các giá trị tương đối nhỏ của n(20 trong ví dụ này), bạn có thể sử dụng một phương thức khai thác thực tế là các số nguyên tự nhiên là sự kết hợp của các bit.

Giải pháp T-SQL

Dữ liệu mẫu:

DECLARE @Sample AS TABLE 
(
    item_id     tinyint IDENTITY(1,1) PRIMARY KEY NONCLUSTERED,
    item        nvarchar(500) NOT NULL,
    bit_value   AS 
                CONVERT
                (
                    integer, 
                    POWER(2, item_id - 1)
                )
                PERSISTED UNIQUE CLUSTERED
);    

INSERT @Sample
    (item)
VALUES
    (N'Ann'),
    (N'Bob'),
    (N'Charles'),
    (N'Darren'),
    (N'Eric'),
    (N'Fred'),
    (N'George'),
    (N'Harry'),
    (N'Ian'),
    (N'John'),
    (N'Keith'),
    (N'Larry'),
    (N'Mark'),
    (N'Nathan'),
    (N'Owen'),
    (N'Paul'),
    (N'Quentin'),
    (N'Ryan'),
    (N'Steve'),
    (N'Terry');

Dung dịch:

-- Maximum integer we need
-- for all combinations of 'n' bits
DECLARE 
    @max integer = 
    POWER(2,
        (
            SELECT COUNT(*) 
            FROM @Sample AS s
        )
    ) - 1;

SELECT
    combination =
        STUFF
        (
            (
                -- Choose items where the bit is set
                -- and concatenate all matches
                SELECT ',' + s.item 
                FROM @Sample AS s
                WHERE
                    n.n & s.bit_value = s.bit_value
                ORDER BY
                    s.bit_value
                FOR XML 
                    PATH (''),
                    TYPE                    
            ).value('(./text())[1]', 'varchar(8000)'), 1, 1, ''
        )
-- A standard numbers table
-- (single column, integers from 1 to 1048576, indexed)
FROM dbo.Numbers AS N
WHERE
    N.n BETWEEN 1 AND @max;

Mẫu đầu ra:

╔════════════════════════╗
║      combination       ║
╠════════════════════════╣
║ Ann                    ║
║ Bob                    ║
║ Ann,Bob                ║
║ Charles                ║
║ Ann,Charles            ║
║ Bob,Charles            ║
║ Ann,Bob,Charles        ║
║ Darren                 ║
║ Ann,Darren             ║
║ Bob,Darren             ║
║ Ann,Bob,Darren         ║
║ Charles,Darren         ║
║ Ann,Charles,Darren     ║
║ Bob,Charles,Darren     ║
║ Ann,Bob,Charles,Darren ║
║ ...                    ║
╚════════════════════════╝

Kế hoạch thực hiện:

Kế hoạch thực hiện

Phải mất 41 giây để viết 1.048.576 kết hợp vào một biến trên máy tính xách tay của tôi. Với tính song song bắt buộc, tôi có thể giảm thời gian thực hiện xuống DOP 8còn 13 giây.

Nếu bạn cần một bảng Số, đây là cách nhanh chóng để tạo một bảng:

SELECT TOP (1048576)
    n = ISNULL(CONVERT(integer, ROW_NUMBER() OVER (ORDER BY (SELECT NULL))), 0)
INTO dbo.Numbers
FROM sys.columns AS c
CROSS JOIN sys.columns AS c2
CROSS JOIN sys.columns AS c3;

CREATE UNIQUE CLUSTERED INDEX cuq
ON dbo.Numbers (n)
WITH (MAXDOP = 1, SORT_IN_TEMPDB = ON);

Giải pháp SQLCLR

Có thể triển khai hiệu quả hơn nhiều trong SQLCLR (SQL Server 2005 trở đi):

CREATE ASSEMBLY [Demo]
    AUTHORIZATION [dbo]
    FROM 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GO
CREATE FUNCTION dbo.Combinations
(
    @ElementsCSV nvarchar (4000)
)
RETURNS TABLE
(
    Combination nvarchar (4000) NULL
)
AS EXTERNAL NAME Demo.UserDefinedFunctions.Permute;

Ví dụ sử dụng:

SELECT 
    f.Combination
FROM dbo.Combinations('A,B,C,D') AS f;

Đầu ra:

╔═════════════╗
║ Combination ║
╠═════════════╣
║ A           ║
║ B           ║
║ A,B         ║
║ C           ║
║ A,C         ║
║ B,C         ║
║ A,B,C       ║
║ D           ║
║ A,D         ║
║ B,D         ║
║ A,B,D       ║
║ C,D         ║
║ A,C,D       ║
║ B,C,D       ║
║ A,B,C,D     ║
╚═════════════╝

Sử dụng bộ 20 phần tử từ trước đó:

DECLARE @Sample AS TABLE 
(
    item_id     tinyint IDENTITY(1,1) PRIMARY KEY CLUSTERED,
    item        nvarchar(50) NOT NULL
);

INSERT @Sample
    (item)
VALUES
    (N'Ann'),
    (N'Bob'),
    (N'Charles'),
    (N'Darren'),
    (N'Eric'),
    (N'Fred'),
    (N'George'),
    (N'Harry'),
    (N'Ian'),
    (N'John'),
    (N'Keith'),
    (N'Larry'),
    (N'Mark'),
    (N'Nathan'),
    (N'Owen'),
    (N'Paul'),
    (N'Quentin'),
    (N'Ryan'),
    (N'Steve'),
    (N'Terry');

Giải pháp SQLCLR:

-- Create CSV input
DECLARE 
    @Elements nvarchar(4000) =
        STUFF
        (
            (
                SELECT ',' + s.item 
                FROM @Sample AS s
                ORDER BY
                    s.item_id
                FOR XML 
                    PATH (''),
                    TYPE                    
            ).value('(./text())[1]', 'varchar(8000)'), 1, 1, ''
        );

DECLARE
    @bitbucket nvarchar(4000);

SELECT
    @bitbucket = combination
FROM dbo.Combinations(@Elements);

Thời gian thực hiện là 2,5 giây cho các kết hợp 1.048.576 trên máy tính xách tay của tôi tại DOP 1.

Tạo đầu vào CSV:

Gói đầu vào CSV

Tìm kiếm sự kết hợp:

Kế hoạch chức năng SQLCLR

Mã nguồn C #:

using System;
using System.Collections;
using Microsoft.SqlServer.Server;

public partial class UserDefinedFunctions
{
    [SqlFunction
        (
        DataAccess=DataAccessKind.None, 
        SystemDataAccess=SystemDataAccessKind.None,
        FillRowMethodName="FillRow",
        TableDefinition="Permutation nvarchar(4000)"
        )
    ]
    public static IEnumerable Permute(string ElementsCSV)
    {
        // Split CSV
        string[] elements = ElementsCSV.Split(new char[] { ',' });

        // Highest integer needed
        int count = (int)Math.Pow(2, elements.Length) - 1;

        // Pre-computed array of 2^n values
        int[] powers = new int[elements.Length];

        for (int i = 0; i < powers.Length; i++)
        {
            powers[i] = (int)Math.Pow(2, i);
        }

        // Test integers
        for (int i = 1; i <= count; i++)
        {
            // Reset output
            string s = string.Empty;

            // Test each bit that could be set
            for (int bit = 0; bit < powers.Length && i >= powers[bit]; bit++)
            {
                if ((i & powers[bit]) == powers[bit])
                {
                    // Add the element corresponding to the set bit
                    s += elements[bit] + ',';
                }
            }

            // Return a row via enumeration
            yield return s.Substring(0, s.Length - 1);
        }
    }

    // Called by SQL Server to fetch a row
    public static void FillRow(object o, out string Permutation)
    {
        Permutation = (string)o;
    }
}

— Paul White nói GoFundMonica
nguồn