Stai cercando distanza Levenshtein
Ecco un'implementazione dell'algoritmo per T-SQL:Calcolo in corso Distanza di Levenshtein in TSQL
Poiché la firma della funzione è come:
CREATE FUNCTION [dbo].[LEVENSHTEIN]( @s NVARCHAR(MAX), @t NVARCHAR(MAX) )
/*
Levenshtein Distance Algorithm: TSQL Implementation
by Joseph Gama
http://www.merriampark.com/ldtsql.htm
Puoi invocarlo nella tua query come:
Select *
from ValuesInDatabase V
order by
[dbo].[LEVENSHTEIN]( V.ClientName, 'Alliance A' )
Non dovresti aspettarti prestazioni elevate.
Modificato
Copio qui la funzione di Joseph Gama per preservarla, non dimenticare di visitare devioblog :
CREATE FUNCTION [dbo].[LEVENSHTEIN]( @s NVARCHAR(MAX), @t NVARCHAR(MAX) )
/*
Levenshtein Distance Algorithm: TSQL Implementation
by Joseph Gama
http://www.merriampark.com/ldtsql.htm
Returns the Levenshtein Distance between strings s1 and s2.
Original developer: Michael Gilleland http://www.merriampark.com/ld.htm
Translated to TSQL by Joseph Gama
Fixed by Herbert Oppolzer / devio
as described in http://devio.wordpress.com/2010/09/07/calculating-levenshtein-distance-in-tsql
*/
RETURNS INT AS
BEGIN
DECLARE @d NVARCHAR(MAX), @LD INT, @m INT, @n INT, @i INT, @j INT,
@s_i NCHAR(1), @t_j NCHAR(1),@cost INT
--Step 1
SET @n = LEN(@s)
SET @m = LEN(@t)
SET @d = REPLICATE(NCHAR(0),(@n+1)*(@m+1))
IF @n = 0
BEGIN
SET @LD = @m
GOTO done
END
IF @m = 0
BEGIN
SET @LD = @n
GOTO done
END
--Step 2
SET @i = 0
WHILE @i <= @n BEGIN
SET @d = STUFF(@d,@i+1,1,NCHAR(@i)) --d(i, 0) = i
SET @i = @i+1
END
SET @i = 0
WHILE @i <= @m BEGIN
SET @d = STUFF(@d,@i*(@n+1)+1,1,NCHAR(@i)) --d(0, j) = j
SET @i = @i+1
END
--Step 3
SET @i = 1
WHILE @i <= @n BEGIN
SET @s_i = SUBSTRING(@s,@i,1)
--Step 4
SET @j = 1
WHILE @j <= @m BEGIN
SET @t_j = SUBSTRING(@t,@j,1)
--Step 5
IF @s_i = @t_j
SET @cost = 0
ELSE
SET @cost = 1
--Step 6
SET @d = STUFF(@d,@j*(@n+1)[email protected]+1,1,
NCHAR(dbo.MIN3(
UNICODE(SUBSTRING(@d,@j*(@n+1)[email protected]+1,1))+1,
UNICODE(SUBSTRING(@d,(@j-1)*(@n+1)[email protected]+1,1))+1,
UNICODE(SUBSTRING(@d,(@j-1)*(@n+1)[email protected]+1,1))[email protected])
))
SET @j = @j+1
END
SET @i = @i+1
END
--Step 7
SET @LD = UNICODE(SUBSTRING(@d,@n*(@m+1)[email protected]+1,1))
done:
RETURN @LD
END
