I've been wondering for months about how to implement this algorithm in Transact SQL, https://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance
How can it be done?
Today I finally stumbled upon this Stack Overflow-answer by leebickmtu showing an implementation in C#, originally ported from Java. I took the liberty to port it to a Transact SQL function, enjoy!
IF OBJECT_ID (N'dbo.InlineMax', N'FN') IS NOT NULL
DROP FUNCTION dbo.InlineMax;
GO
CREATE FUNCTION dbo.InlineMax(@valueOne int, @valueTwo int)
RETURNS FLOAT
AS
BEGIN
IF @valueOne > @valueTwo
BEGIN
RETURN @valueOne
END
RETURN ISNULL(@valueTwo, @valueOne)
END;
GO
IF OBJECT_ID (N'dbo.InlineMin', N'FN') IS NOT NULL
DROP FUNCTION dbo.InlineMin;
GO
CREATE FUNCTION dbo.InlineMin(@valueOne int, @valueTwo int)
RETURNS FLOAT
AS
BEGIN
IF @valueOne < @valueTwo
RETURN @valueOne
RETURN @valueTwo
END;
GO
IF OBJECT_ID (N'dbo.JaroWinklerDistance', N'FN') IS NOT NULL
DROP FUNCTION dbo.JaroWinklerDistance;
GO
CREATE FUNCTION dbo.JaroWinklerDistance(@stringOne varchar(MAX), @stringTwo varchar(MAX))
RETURNS FLOAT
WITH EXECUTE AS CALLER
AS
BEGIN
DECLARE @mWeightThreshold FLOAT; SET @mWeightThreshold = 0.7;
DECLARE @mNuMChars INT; SET @mNumChars = 4;
DECLARE @lLen1 int; SET @lLen1 = LEN(@stringOne)
DECLARE @lLen2 int; SET @lLen2 = LEN(@stringTwo)
IF @lLen1 = 0
RETURN CASE WHEN @lLen2 = 0 THEN 1 ELSE 0 END
DECLARE @lSearchRange int; SET @lSearchRange = dbo.InlineMax(0,dbo.InlineMax(@lLen1, @lLen2)/2 - 1);
DECLARE @lMatched1 TABLE (position int not null, [status] bit not null)
DECLARE @lMatched2 TABLE (position int not null, [status] bit not null)
DECLARE @lNumCommon int; SET @lNumCommon = 0
DECLARE @i int; SET @i = 1; WHILE(@i <= @lLen1)
BEGIN
DECLARE @lStart int; SET @lStart = dbo.InlineMax(1, @i - @lSearchRange)
DECLARE @lEnd int; SET @lEnd = dbo.InlineMin(@i + @lSearchRange + 1, @lLen2)
DECLARE @j int; SET @j = @lStart; WHILE(@j <= @lEnd)
BEGIN
IF((SELECT [status] FROM @lMatched2 WHERE position = @j) = 1)
BEGIN
SET @j = @j + 1
CONTINUE
END
IF (SELECT SUBSTRING(@stringOne, @i, 1)) <> (SELECT SUBSTRING(@stringTwo, @j, 1))
BEGIN
SET @j = @j + 1
CONTINUE
END
INSERT INTO @lMatched1 (position, [status]) VALUES(@i, 1)
INSERT INTO @lMatched2 (position, [status]) VALUES(@j, 1)
SET @lNumCommon = @lNumCommon + 1
BREAK
END
SET @i = @i + 1
END
IF @lNumCommon = 0
BEGIN
RETURN 0.0;
END
DECLARE @lNumHalfTransposed int; SET @lNumHalfTransposed = 0
DECLARE @k INT; SET @k = 1;
DECLARE @stopLoop bit; SET @stopLoop = 0;
SET @i = 1; WHILE(@i <= @lLen1)
BEGIN
IF ((SELECT [status] FROM @lMatched1 WHERE position = @i) = 1)
BEGIN
SET @i = @i + 1
CONTINUE;
END
WHILE(@stopLoop = 0)
BEGIN
IF((SELECT [status] FROM @lMatched2 WHERE position = @k) = 0)
SET @k = @k + 1
ELSE
BREAK
IF((SELECT SUBSTRING(@stringOne, @i, 1)) <> (SELECT SUBSTRING(@stringTwo, @k, 1)))
SET @lNumHalfTransposed = @lNumHalfTransposed + 1
SET @k = @k + 1
END
SET @i = @i + 1
END
DECLARE @lNumTransposed INT; SET @lNumTransposed = @lNumHalfTransposed/2;
DECLARE @lNumCommonD FLOAT; SET @lNumCommonD = @lNumCommon
DECLARE @lWeight FLOAT; SET @lWeight = (@lNumCommonD / @lLen1 + @lNumCommonD / @lLen2 + (@lNumCommon - @lNumTransposed) / @lNumCommonD) / 3.0;
IF(@lWeight <= @mWeightThreshold)
RETURN @lWeight
DECLARE @lMax INT; SET @lMax = dbo.InlineMin(@mNumChars, dbo.InlineMin(@lLen1, @lLen2))
DECLARE @lPos INT; SET @lPos = 0
WHILE(@lPos < @lMax AND (SELECT SUBSTRING(@stringOne, @lPos, 1)) = (SELECT SUBSTRING(@stringTwo, @lPos, 1)))
BEGIN
SET @lPos = @lPos + 1
END
IF @lPos = 0
RETURN @lWeight
RETURN @lWeight + 0.1 * @lPos * (1.0 - @lWeight)
END;
GO