SQL 函数 - 使用 Levenshtein 距离算法进行模糊匹配 - 仅返回最小值答案

【问题标题】：SQL Function - Fuzzy Matching with Levenshtein Distance Algorithm - Return Lowest Value OnlySQL 函数 - 使用 Levenshtein 距离算法进行模糊匹配 - 仅返回最小值
【发布时间】：2019-12-18 13:25:51
【问题描述】：

问题：需要 SQL 函数使用 Levenshtein 算法返回“最低”匹配值。

代码：


CREATE FUNCTION ufn_levenshtein(@s1 nvarchar(3999), @s2 nvarchar(3999))
RETURNS int
AS
BEGIN
 DECLARE @s1_len int, @s2_len int
 DECLARE @i int, @j int, @s1_char nchar, @c int, @c_temp int
 DECLARE @cv0 varbinary(8000), @cv1 varbinary(8000)

 SELECT
  @s1_len = LEN(@s1),
  @s2_len = LEN(@s2),
  @cv1 = 0x0000,
  @j = 1, @i = 1, @c = 0

 WHILE @j <= @s2_len
  SELECT @cv1 = @cv1 + CAST(@j AS binary(2)), @j = @j + 1

 WHILE @i <= @s1_len
 BEGIN
  SELECT
   @s1_char = SUBSTRING(@s1, @i, 1),
   @c = @i,
   @cv0 = CAST(@i AS binary(2)),
   @j = 1

  WHILE @j <= @s2_len
  BEGIN
   SET @c = @c + 1
   SET @c_temp = CAST(SUBSTRING(@cv1, @j+@j-1, 2) AS int) +
    CASE WHEN @s1_char = SUBSTRING(@s2, @j, 1) THEN 0 ELSE 1 END
   IF @c > @c_temp SET @c = @c_temp
   SET @c_temp = CAST(SUBSTRING(@cv1, @j+@j+1, 2) AS int)+1
   IF @c > @c_temp SET @c = @c_temp
   SELECT @cv0 = @cv0 + CAST(@c AS binary(2)), @j = @j + 1
 END

 SELECT @cv1 = @cv0, @i = @i + 1
 END

 RETURN @c
END




IF OBJECT_ID('tempdb..#ExistingCustomers') IS NOT NULL
    DROP TABLE #ExistingCustomers;

    CREATE TABLE #ExistingCustomers
(
    Customer VARCHAR(255),
    ID INT
)

INSERT #ExistingCustomers SELECT 'Ed''s Barbershop',  1002
INSERT #ExistingCustomers SELECT 'GroceryTown',  1003
INSERT #ExistingCustomers SELECT 'Candy Place',  1004
INSERT #ExistingCustomers SELECT 'Handy Man',  1005



IF OBJECT_ID('tempdb..#POTENTIALCUSTOMERS') IS NOT NULL
    DROP TABLE #POTENTIALCUSTOMERS;

CREATE TABLE #POTENTIALCUSTOMERS(Customer VARCHAR(255));

INSERT #POTENTIALCUSTOMERS SELECT 'Eds Barbershop'
INSERT #POTENTIALCUSTOMERS SELECT 'Grocery Town'
INSERT #POTENTIALCUSTOMERS SELECT 'Candy Place'
INSERT #POTENTIALCUSTOMERS SELECT 'Handee Man'
INSERT #POTENTIALCUSTOMERS SELECT 'The Apple Farm'
INSERT #POTENTIALCUSTOMERS SELECT 'Ride-a-Long Bikes'


SELECT A.Customer,
       b.ID,
       b.Customer as cust,
       dbo.ufn_levenshtein(REPLACE(A.Customer, ' ', ''), REPLACE(B.Customer, ' ', '')) as ValueLev
FROM #POTENTIALCUSTOMERS a
     LEFT JOIN #ExistingCustomers b ON dbo.ufn_levenshtein(REPLACE(A.Customer, ' ', ''), REPLACE(B.Customer, ' ', '')) < 15;

这会返回：

我想退货：

说明：结果是 Levenshtein 算法的“最低”值。有两行 Levenshtein 分数相同 The Apple Farm 和 Ride-a-Long Bikes，在这种情况下，任何值都可以，只要它是一个值。

参考文献：

SQL Fuzzy Join - MSSQL

http://www.kodyaz.com/articles/fuzzy-string-matching-using-levenshtein-distance-sql-server.aspx

【问题讨论】：

标签： sql sql-server algorithm function

【解决方案1】：

如果您按潜在客户分区并使用 ValueLev 对结果进行排序，您可以使用 CTE 获得您想要的结果：

;WITH CTE AS
(
    SELECT  RANK() OVER (PARTITION BY a.Customer ORDER BY dbo.ufn_levenshtein(REPLACE(A.Customer, ' ', ''), REPLACE(B.Customer, ' ', '')) ASC) AS RowNbr,
            A.Customer,
            b.ID,
            b.Customer as cust,
            dbo.ufn_levenshtein(REPLACE(A.Customer, ' ', ''), REPLACE(B.Customer, ' ', '')) as ValueLev
      FROM  #POTENTIALCUSTOMERS a
        LEFT JOIN #ExistingCustomers b ON dbo.ufn_levenshtein(REPLACE(A.Customer, ' ', ''), REPLACE(B.Customer, ' ', '')) < 15
)
SELECT  Customer,
        MIN(ID) AS ID,
        MIN(cust) AS cust,
        ValueLev
  FROM  CTE
  WHERE CTE.RowNbr = 1
  GROUP BY Customer, ValueLev

由于您不介意在 ValueLev 重复的情况下返回哪个结果，请使用 GROUP BY 和 MIN 将结果缩减为每个潜在客户一个。

输出：

Customer            ID      cust            ValueLev
Candy Place         1004    Candy Place     0
Grocery Town        1003    GroceryTown     0
Eds Barbershop      1002    Ed's Barbershop 1
Handee Man          1005    Handy Man       2
The Apple Farm      1004    Candy Place     9
Ride-a-Long Bikes   1003    Candy Place     14

【讨论】：