SQL Server对比两字符串的相似度（函数算法）

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一、概述

最近有人问到关于两个字符串求相似度的函数，所以就写了本篇文章，分别是“简单的模糊匹配”，“顺序匹配”，“一对一位置匹配”。在平时的这种函数可能会需要用到，业务需求不一样，这里只给出参照，实际情况可以相应修改。本文所有的两个字段比较都是除以比较字段本身，例如A与B比较，找出的长度除以A的长度，因为考虑如果A的长度大于B的长度，相似度会超100%，例如‘abbc’,'ab'.

如果大家想除以B的长度，只需要在语句末尾将‘SET @num=@num*1.0/LEN(@Cloumna)’修改成‘SET @num=@num*1.0/LEN(@Cloumnb)’

1.两个字符串简单相似

---两个字段简单相似
CREATE FUNCTION DBO.FN_Resemble
(@Cloumna NVARCHAR(MAX),
@Cloumnb NVARCHAR(MAX)
)
RETURNS FLOAT
AS
BEGIN
DECLARE @num FLOAT,@len int
SET @Cloumna=ISNULL(@Cloumna,0)
SET @Cloumnb=ISNULL(@Cloumnb,0)
SET @len=1
SET @num=0
WHILE(LEN(@Cloumna)<>0 AND LEN(@CloumnB)<>0)
BEGIN
WHILE(@len<=LEN(@Cloumna))
BEGIN
DECLARE @a NVARCHAR(4)
SET @a=''
SET @a=SUBSTRING(@Cloumna,@len,1)
IF(CHARINDEX(@a,@CloumnB)>0)
BEGIN
SET @num=@num+1
END
SET @len=@len+1
END
SET @num=@num*1.0/LEN(@Cloumna)
BREAK
END RETURN @num
END----测试代码
SELECT DBO.FN_Resemble('ABDC321G','ABDC123G')

2.两个字符串顺序相似

---两个字段顺序相似
CREATE FUNCTION DBO.FN_Resemble_order
(@Cloumna NVARCHAR(MAX),
@Cloumnb NVARCHAR(MAX)
)
RETURNS FLOAT
AS
BEGIN
DECLARE @num FLOAT,@len int
SET @Cloumna=ISNULL(@Cloumna,0)
SET @Cloumnb=ISNULL(@Cloumnb,0)
SET @len=1
SET @num=0
WHILE(LEN(@Cloumna)<>0 AND LEN(@CloumnB)<>0)
BEGIN
DECLARE @a NVARCHAR(4)
DECLARE @b NVARCHAR(4)
IF(LEN(@Cloumna)>=LEN(@CloumnB))
BEGIN
WHILE(@len<=LEN(@CloumnB))
BEGIN SET @a=''
SET @a=SUBSTRING(@Cloumna,@len,1)
SET @b=''
SET @b=SUBSTRING(@CloumnB,@len,1)
IF(@a=@b)
BEGIN
SET @num=@num+1
END
ELSE
BEGIN
break
END
SET @len=@len+1
END
END
ELSE IF (LEN(@Cloumna)<LEN(@CloumnB))
BEGIN
WHILE(@len<=LEN(@Cloumna))
BEGIN
SET @a=''
SET @a=SUBSTRING(@Cloumna,@len,1)
SET @b=''
SET @b=SUBSTRING(@CloumnB,@len,1)
IF(@a=@b)
BEGIN
SET @num=@num+1
END
ELSE
BEGIN
break
END
SET @len=@len+1
END END
SET @num=@num*1.0/LEN(@Cloumna)
BREAK
END
RETURN @num
END
go----测试代码
SELECT DBO.FN_Resemble_order('ABDC456G','ABDC123G')

3.两个字符串一对一相似

---两个字段一对一相似
CREATE FUNCTION DBO.FN_Resemble_onebyone
(@Cloumna NVARCHAR(MAX),
@Cloumnb NVARCHAR(MAX)
)
RETURNS FLOAT
AS
BEGIN
DECLARE @num FLOAT,@len int
SET @Cloumna=ISNULL(@Cloumna,0)
SET @Cloumnb=ISNULL(@Cloumnb,0)
SET @len=1
SET @num=0
WHILE(LEN(@Cloumna)<>0 AND LEN(@CloumnB)<>0)
BEGIN
DECLARE @a NVARCHAR(4)
DECLARE @b NVARCHAR(4)
IF(LEN(@Cloumna)>=LEN(@CloumnB))
BEGIN
WHILE(@len<=LEN(@CloumnB))
BEGIN SET @a=''
SET @a=SUBSTRING(@Cloumna,@len,1)
SET @b=''
SET @b=SUBSTRING(@CloumnB,@len,1)
IF(@a=@b)
BEGIN
SET @num=@num+1
END
SET @len=@len+1
END
END
ELSE IF (LEN(@Cloumna)<LEN(@CloumnB))
BEGIN
WHILE(@len<=LEN(@Cloumna))
BEGIN
SET @a=''
SET @a=SUBSTRING(@Cloumna,@len,1)
SET @b=''
SET @b=SUBSTRING(@CloumnB,@len,1)
IF(@a=@b)
BEGIN
SET @num=@num+1
END
SET @len=@len+1
END END
SET @num=@num*1.0/LEN(@Cloumna)
BREAK
END
RETURN @num
END----测试代码
SELECT DBO.FN_Resemble_onebyone('ABDC456G','ABDC123G')

4.对比两个版本号的大小

如果前面比后面的大返回1，小返回-1，相等返回0

ALTER FUNCTION FNStrCompare
(@Val1 VARCHAR(50),---比较字符串1
@Val2 VARCHAR(50),---比较字符串2
@Break VARCHAR(10) ---分隔符
)
RETURNS INT
AS
BEGIN
DECLARE @Num1 INT
DECLARE @Num2 INT
DECLARE @Val1Num INT
DECLARE @Val2Num INT
DECLARE @a INT
IF CHARINDEX(@Break,@Val1)>0 AND CHARINDEX(@Break,@Val2)>0
BEGIN
WHILE LEN(@Val1)>0 AND LEN(@Val2)>0
BEGIN
IF CHARINDEX(@Break,@Val1)>0 AND CHARINDEX(@Break,@Val2)>0
BEGIN
SET @Num1=CHARINDEX(@Break,@Val1)-1
SET @Val1Num=LEFT(@Val1,@Num1)
SET @Val1=SUBSTRING(@Val1,@Num1+2,LEN(@Val1)) SET @Num2=CHARINDEX(@Break,@Val2)-1
SET @Val2Num=LEFT(@Val2,@Num2)
SET @Val2=SUBSTRING(@Val2,@Num1+2,LEN(@Val2)) END
ELSE
BEGIN
SET @Val1Num=CONVERT(INT,@Val1)
SET @Val2Num=CONVERT(INT,@Val2) IF @Val1Num=@Val2Num
BEGIN
SET @a=0
BREAK
END END IF @Val1Num>@Val2Num
BEGIN
SET @a=1
BREAK
END
IF @Val1Num<@Val2Num
BEGIN
SET @a=-1
BREAK
END END
END
ELSE
BEGIN
SET @Val1Num=CONVERT(INT,@Val1)
SET @Val2Num=CONVERT(INT,@Val2)
IF @Val1Num>@Val2Num
BEGIN
SET @a=1
END
IF @Val1Num<@Val2Num
BEGIN
SET @a=-1
END
IF @Val1Num=@Val2Num
BEGIN
SET @a=0
END ENDRETURN @aEND

执行

SELECT chenmh.dbo.FNStrCompare('1.15.1','1.15.1','.')SELECT chenmh.dbo.FNStrCompare('1.15.2','1.15.1','.')SELECT chenmh.dbo.FNStrCompare('1.15.2','2.3.1','.')SELECT chenmh.dbo.FNStrCompare('1.08.2','1.15.1','.')SELECT dbo.FNStrCompare('','','.')