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What exactly and on what basis does the soundex function returns the integer values.
I read through msdn but it only tells that it doesn't considers vowels in the strings.
But what I exactly want to know is what logic is used during comparison of two strings behind th scene.




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There's an entry in Wikipedia about soundex. It has what you're looking for.
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Thanks. This is exactly what I am looking for




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Here is my first attempt to make soundex more selective:
Algorithm sqlserver uses: Replace consonants with digits as follows (but do not change the first letter): b, f, p, v => 1 c, g, j, k, q, s, x, z => 2 d, t => 3 l => 4 m, n => 5 r => 6 Collapse adjacent identical digits into a single digit of that value. Remove all nondigits after the first letter. Return the starting letter and the first three remaining digits. If needed, append zeroes to make it a letter and three digits.
Lets extend this to 5 in length to make it more selective. On lastname data I see a selectivity increase from 1 in 3000 to 1 in 10000.
Function contains no error checking and is not optimized.
drop function dbo.soundex5; go
create function Soundex5( @name varchar(30)) returns varchar(5) as begin
declare @out varchar(20), @i int, @vc varchar(1);
set @name = @name + '00000';
set @out = left(@name,1);
set @i = 2; while @i <= len(@name) begin set @vc = substring(@name, @i, 1)
set @out = @out + case when charindex(@vc, 'bfpv') > 0 then '1' when charindex(@vc, 'cgjkqsxz') > 0 then '2' when charindex(@vc, 'dt') > 0 then '3' when charindex(@vc, 'l') > 0 then '4' when charindex(@vc, 'mn') > 0 then '5' when charindex(@vc, 'r') > 0 then '6' when charindex(@vc, '0') > 0 then '0' else '' end;
set @i = @i + 1; end
 ignore similar consecutive sounds set @out = REPLACE(@out,'11','1'); set @out = REPLACE(@out,'22','2'); set @out = REPLACE(@out,'33','3'); set @out = REPLACE(@out,'44','4'); set @out = REPLACE(@out,'55','5'); set @out = REPLACE(@out,'66','6');
return left(@out,5);
end go



