Untuk nilai yang relatif kecil n(20 dalam contoh ini), Anda dapat menggunakan metode yang mengeksploitasi fakta bahwa bilangan bulat alami adalah kombinasi bit.
Solusi T-SQL
Contoh data:
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');
Larutan:
-- 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;
Sampel keluaran:
╔════════════════════════╗
║ 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 ║
║ ... ║
╚════════════════════════╝
Rencana eksekusi:
Butuh 41 detik untuk menulis 1.048.576 kombinasi ke variabel di laptop saya. Dengan paralelisme paksa, saya dapat menurunkan waktu eksekusi DOP 8menjadi 13 detik.
Jika Anda membutuhkan tabel Angka, ini adalah cara cepat untuk menghasilkannya:
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);
Solusi SQLCLR
Implementasi yang jauh lebih efisien dimungkinkan di SQLCLR (SQL Server 2005 dan seterusnya):
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;
Contoh penggunaan:
SELECT
f.Combination
FROM dbo.Combinations('A,B,C,D') AS f;
Keluaran:
╔═════════════╗
║ 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 ║
╚═════════════╝
Menggunakan set 20-elemen dari sebelumnya:
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');
Solusi 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);
Waktu eksekusi adalah 2,5 detik untuk 1.048.576 kombinasi di laptop saya di DOP 1.
Membuat input CSV:
Menemukan kombinasi:
C # Kode Sumber:
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;
}
}
