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Nice article! I really had to "think" my way through this one, but its likely to be very useful.
John Scarborough MCDBA, MCSA




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Forget that horrible procdural code. Let Sequence be a table of (n) integers from 1 to (n): SELECT S1.i, S2.i, .., Sn1.i FROM Sequence AS S1, Sequence AS S2, ..Sequence AS Sn WHERE S1.i NOT IN (S2.i, .., Sn.i) AND S2.i NOT IN (S1.i, .., Sn.i) . AND Sn.i NOT IN (S1.i, .., S[n1].i); There are some other tricks for assigning a combination number to the rows. Most of this guy's poostngs have been procedural code and not good SQL at all.
Books in Celko Series for MorganKaufmann Publishing Analytics and OLAP in SQL Data and Databases: Concepts in Practice Data, Measurements and Standards in SQL SQL for Smarties SQL Programming Style SQL Puzzles and Answers Thinking in Sets Trees and Hierarchies in SQL




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I have to finish my own posting. If you have SQL2005 and you can use a CTE for the Sequence table. Now load the results in a table. Perm(i1, i2, ..in) with a primary key of all columns. Once you have this table for all permutations of (n), you can create a set of views like this whch will give you the permutatiosn for (j < n). For example (j=5) is done with this: CREATE VIEW Perm5 (i1, i2, i3, i4, i5) AS SELECT DISTINCT i1, i2, i3, i4, i5 FROM Perm WHERE i1 <= 5 AND i2 <= 5 AND i3 <= 5 AND i4 <= 5 AND i5 <= 5; Think in sets and not in procedrual code.
Books in Celko Series for MorganKaufmann Publishing Analytics and OLAP in SQL Data and Databases: Concepts in Practice Data, Measurements and Standards in SQL SQL for Smarties SQL Programming Style SQL Puzzles and Answers Thinking in Sets Trees and Hierarchies in SQL




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I think it is better to limit the input parameter @n <= 10. I modify this proc in my SQL 2000 Query Analyzer just change the length of all parameters such as @sqlStmt,@base etc. to 5000 Then,I used 11 as input parameter and the Query Analyzer return an error: can't generate query plan...... But I didn't try 10......




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I see nothing wrong with procedural code if implemeneted properly. The original code has the problem of being too complex and is also limited in scope. I ran it up to 7, beyond which my SQL2000 will not be able to generate a plan. The procedure below is inspired by the original code but is drastically different: it handles large set really fast and dynamic SQL statement is short and recursive (use @debug = 1 to see it). To use it, you need to store your values in a table with a single column 'x'. This procedure permutes r out of n. Of course you need to make sure r<=n, and be aware that the result set could be substantial (n! / (nr)! permutations). It may not be useful, but just for fun. Create Proc sp_permutate (@n smallint, @t varchar(8), @debug bit = 0) as begin set nocount on declare @sqlStmt varchar(4000), @delim varchar(2) declare @i int declare @j int if @debug = 1 set @delim = char(10) else set @delim = '' set @sqlStmt = 'SELECT x' + cast(@n as varchar(2)) + '=X from ' + @t + @delim set @i = @n 1 while @i > 0 Begin set @j = @n set @sqlStmt = 'SELECT x' + cast(@i as varchar(2)) + '=X, T.* from ' + @t + ' join (' + @delim + @sqlStmt + ') T on x<>x' + cast(@j as varchar(2)) set @j = @j  1 while @j > @i Begin set @sqlStmt = @sqlStmt + ' and x<>x' + cast(@j as varchar(2)) set @j = @j  1 End set @sqlStmt = @sqlStmt + @delim set @i = @i  1 End print @sqlStmt exec (@sqlStmt) set nocount off end go




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SQL 2005 has CTE that can do the permutations more easy I coded for SQL2000 , If you use a phisical table and not a "memory table" like (select 1 union select 2 union ........) then the optimizer will crush for more than 10 join with the table to itself so memory derived tables must be used on this one




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Technically, you should be using Standard SQL/PSM instead of proprietary TSQL, since it is the proper way to implement procedures. But the whole idea of SQL is that we are using a declarative language and not a procedural one. The nice thing about building a table is that you do it one time only and you can use any procedural language you wish  even TSQL. Of course 10! = 3,628,800 which is a fair size table, but not impossible.
Books in Celko Series for MorganKaufmann Publishing Analytics and OLAP in SQL Data and Databases: Concepts in Practice Data, Measurements and Standards in SQL SQL for Smarties SQL Programming Style SQL Puzzles and Answers Thinking in Sets Trees and Hierarchies in SQL




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Hi all,
I wrote this for fun, and thought I'd share it here, since it's vaguely related. It's interesting mathematics (in that the method works) if nothing else.
If you set @i below to your set size, then a list of all combinations of numbers is returned (as a varchar). e.g. @i = 3 gives:
210 201 120 021 102 012
The timings on my pc are: Size Seconds Rows 7 0 5040 8 1 40320 9 6 362880 10 60 3628800
This SQL script is safe to run Inputs DECLARE @i TINYINT SET @i = 7 set size Validation IF @i > 10 BEGIN PRINT 'i is too large' SET @i = 0 END Declarations CREATE TABLE #t (n TINYINT, v VARCHAR(10)) CREATE CLUSTERED INDEX #ix_t ON #t (n) DECLARE @n TABLE (i TINYINT) numbers table DECLARE @Counter INT Initialisations INSERT @n SELECT 0 INSERT #t SELECT 0, '0 ' SET @Counter = 1 Loop for each integer from 1 to @i1 WHILE @Counter <= @i  1 BEGIN INSERT @n SELECT @Counter INSERT #t SELECT @Counter, STUFF(v, i+1, 0, @Counter) FROM #t, @n WHERE n = @Counter  1 SET @Counter = @Counter + 1 END Select results we're interested in SELECT v FROM #t WHERE n = @i  1 Tidy up DROP TABLE #t
Ryan Randall
Solutions are easy. Understanding the problem, now, that's the hard part.




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Just to toss my hat in the ring...
create procedure dbo.usp_permutate @charset nvarchar(256) = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' as
set nocount on
 a set of all values in the charset create table #set ( k int, v nchar(1) )
declare @i int, @c nvarchar(5) declare @select nvarchar(4000) declare @from nvarchar(4000)
select @i = 1 , @select = 's1.v ' , @from = '#set s1 '
insert into #set ( k, v ) values ( 1, substring(@charset, @i, 1) )
while @i < len(@charset) begin
set @i = @i + 1 set @c = convert(nvarchar(5), @i)
insert into #set ( k, v ) values ( 1, substring(@charset, @i, 1) ) set @select = @select + '+ s' + @c + '.v ' set @from = @from + 'join #set s' + @c + ' on s' + @c + '.k = s1.k '
end
 output query exec( 'select ' + @select + 'as permutation from ' + @from + 'order by permutation' )
 clean up drop table #set



