n(इस उदाहरण में 20) के अपेक्षाकृत छोटे मूल्यों के लिए, आप एक ऐसी विधि का उपयोग कर सकते हैं जो इस तथ्य का फायदा उठाती है कि प्राकृतिक पूर्णांक बिट्स के संयोजन हैं।
टी-SQL समाधान
नमूना डेटा:
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');
समाधान:
-- 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;
आउटपुट नमूना:
╔════════════════════════╗
║ 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 ║
║ ... ║
╚════════════════════════╝
निष्पादन योजना:
मेरे लैपटॉप पर एक चर में 1,048,576 संयोजनों को लिखने में 41 सेकंड लगते हैं । मजबूर समानतावाद के साथ, मैं निष्पादन समय को 13 सेकंड तक छोड़ने में सक्षम था ।DOP 8
यदि आपको संख्या तालिका की आवश्यकता है, तो यह एक त्वरित तरीका है:
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);
SQLCLR समाधान
SQLCLR (SQL Server 2005 आगे) में बहुत अधिक कुशल कार्यान्वयन संभव है:
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;
उदाहरण का उपयोग:
SELECT
f.Combination
FROM dbo.Combinations('A,B,C,D') AS f;
आउटपुट:
╔═════════════╗
║ 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 ║
╚═════════════╝
पहले से निर्धारित 20-तत्व का उपयोग करना:
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');
SQLCLR समाधान:
-- 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);
मेरे लैपटॉप पर 1,048,576 संयोजनों के लिए निष्पादन समय 2.5 सेकंड है ।DOP 1
CSV इनपुट बनाना:
संयोजन ढूंढना:
C # स्रोत कोड:
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;
}
}