14. 类似正则表达式的字符处理问题

2017-10-31 11:30:46来源:cnblogs.com作者:张骞人点击

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SQL Serve提供了简单的字符模糊匹配功能,比如:like, patindex,不过对于某些字符处理场景还显得并不足够,日常碰到的几个问题有:

  • 1. 同一个字符/字符串,出现了多少次
  • 2. 同一个字符,第N次出现的位置
  • 3. 多个相同字符连续,合并为一个字符
  • 4. 是否为有效IP/身份证号/手机号等

 

. 同一个字符/字符串,出现了多少次

同一个字符,将其替换为空串,即可计算

declare @text varchar(1000)declare @str  varchar(10)set @text = 'ABCBDBE'set @str = 'B'select len(@text) - len(replace(@text,@str,''))

同一个字符串,仍然是替换,因为是多个字符,方法1替换后需要做一次除法;方法2替换时增加一个字符,则不需要

--方法1declare @text varchar(1000)declare @str  varchar(10)set @text = 'ABBBCBBBDBBBE'set @str = 'BBB'select (len(@text) - len(replace(@text,@str,'')))/len(@str)--方法2declare @text varchar(1000)declare @str  varchar(10)set @text = 'ABBBCBBBDBBBE'set @str = 'BBB'select len(replace(@text,@str,@str+'_')) - len(@text)

. 同一个字符/字符串,第N次出现的位置

SQL SERVER定位字符位置的函数为CHARINDEX:

CHARINDEX ( expressionToFind , expressionToSearch [ , start_location ] )

可以从指定位置起开始检索,但是不能取第N次出现的位置,需要自己写SQL来补充,有以下几种思路:

1. 自定义函数, 循环中每次为charindex加一个计数,直到为N

if object_id('NthChar','FN') is not null    drop function NthcharGOcreate function NthChar(@source_string as nvarchar(4000), @sub_string    as nvarchar(1024),@nth           as int) returns int as begin     declare @postion int     declare @count   int     set @postion = CHARINDEX(@sub_string, @source_string)     set @count = 0       while @postion > 0     begin         set @count = @count + 1         if @count = @nth         begin             break         end        set @postion = CHARINDEX(@sub_string, @source_string, @postion + 1)     End     return @postion end GO--select dbo.NthChar('abcabc','abc',2)--4

2. 通过CTE,对待处理的整个表字段操作, 递归中每次为charindex加一个计数,直到为N

if  object_id('tempdb..#T') is not null    drop table #Tcreate table #T(source_string nvarchar(4000))insert into #T values (N'我们我们')insert into #T values (N'我我哦我')declare @sub_string nvarchar(1024)declare @nth        intset @sub_string = N'我们'set @nth = 2;with T(source_string, starts, pos, nth) as (    select source_string, 1, charindex(@sub_string, source_string), 1 from #t    union all    select source_string, pos + 1, charindex(@sub_string, source_string, pos + 1), nth+1 from T    where pos > 0)select     source_string, pos, nthfrom Twhere pos <> 0  and nth = @nthorder by source_string, starts--source_string    pos    nth--我们我们    3    2

3. 借助数字表 (tally table),到不同起点位置去做charindex,需要先自己构造个数字表

--numbers/tally tableIF EXISTS (select * from dbo.sysobjects where id = object_id(N'[dbo].[Numbers]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)    DROP TABLE dbo.Numbers--===== Create and populate the Tally table on the fly SELECT TOP 1000000         IDENTITY(int,1,1) AS number   INTO dbo.Numbers   FROM master.dbo.syscolumns sc1,        master.dbo.syscolumns sc2--===== Add a Primary Key to maximize performance  ALTER TABLE dbo.Numbers        ADD CONSTRAINT PK_numbers_number PRIMARY KEY CLUSTERED (number)--===== Allow the general public to use it  GRANT SELECT ON dbo.Numbers TO PUBLIC--以上数字表创建一次即可,不需要每次都重复创建DECLARE @source_string    nvarchar(4000),         @sub_string       nvarchar(1024),         @nth              intSET @source_string = 'abcabcvvvvabc'SET @sub_string = 'abc'SET @nth = 2 ;WITH T AS(            SELECT ROW_NUMBER() OVER(ORDER BY number) AS nth,       number AS [Position In String]  FROM dbo.Numbers n  WHERE n.number <= LEN(@source_string)       AND CHARINDEX(@sub_string, @source_string, n.number)-number = 0   ----OR   --AND SUBSTRING(@source_string,number,LEN(@sub_string)) = @sub_string) SELECT * FROM T WHERE nth = @nth

4. 通过CROSS APPLY结合charindex,适用于N值较小的时候,因为CROSS APPLY的次数要随着N的变大而增加,语句也要做相应的修改

declare @T table(source_string nvarchar(4000))insert into @T values('abcabc'),('abcabcvvvvabc')declare @sub_string nvarchar(1024)set @sub_string = 'abc'select source_string,       p1.pos as no1,       p2.pos as no2,       p3.pos as no3from @Tcross apply (select (charindex(@sub_string, source_string))) as P1(Pos)cross apply (select (charindex(@sub_string, source_string, P1.Pos+1))) as P2(Pos)cross apply (select (charindex(@sub_string, source_string, P2.Pos+1))) as P3(Pos)

5. 在SSIS里有内置的函数,但T-SQL中并没有

--FINDSTRING in SQL Server 2005 SSISFINDSTRING([yourColumn], "|", 2),--TOKEN in SQL Server 2012 SSISTOKEN(Col1,"|",3)

注:不难发现,这些方法和字符串拆分的逻辑是类似的,只不过一个是定位,一个是截取,如果要获取第N个字符左右的一个/多个字符,有了N的位置,再结合substring去截取即可;

. 多个相同字符连续,合并为一个字符

最常见的就是把多个连续的空格合并为一个空格,解决思路有两个:

1. 比较容易想到的就是用多个replace

但是究竟需要replace多少次并不确定,所以还得循环多次才行

--把两个连续空格替换成一个空格,然后循环,直到charindex检查不到两个连续空格declare @str varchar(100)set @str='abc        abc     kljlk     kljkl'while(charindex('  ',@str)>0)begin    select @str=replace(@str,'  ',' ')endselect @str

2. 按照空格把字符串拆开

对每一段拆分开的字符串trim或者replace后,再用一个空格连接,有点繁琐,没写代码示例,如何拆分字符串可参考:“第N次出现的位置”;

. 是否为有效IP/身份证号/手机号等

类似IP/身份证号/手机号等这些字符串,往往都有自身特定的规律,通过substring去逐位或逐段判断是可以的,但SQL语句的方式往往性能不佳,建议尝试正则函数,见下。

. 正则表达式函数

1. Oracle

从10g开始,可以在查询中使用正则表达式,它通过一些支持正则表达式的函数来实现:

Oracle 10 g

REGEXP_LIKE

REGEXP_REPLACE

REGEXP_INSTR

REGEXP_SUBSTR

Oracle 11g (新增)

REGEXP_COUNT

Oracle用REGEXP函数处理上面几个问题:

(1) 同一个字符/字符串,出现了多少次

select length(regexp_replace('123-345-566', '[^-]', '')) from dual;select REGEXP_COUNT('123-345-566', '-') from dual; --Oracle 11g

(2) 同一个字符/字符串,第N次出现的位置

不需要正则,ORACLE的instr可以直接查找位置:

instr('source_string','sub_string' [,n][,m])

n表示从第n个字符开始搜索,缺省值为1,m表示第m次出现,缺省值为1。

select instr('abcdefghijkabc','abc', 1, 2) position from dual; 

(3) 多个相同字符连续,合并为一个字符

select regexp_replace(trim('agc f   f  '),'/s+',' ') from dual;

(4) 是否为有效IP/身份证号/手机号等

--是否为有效IPWITH IPAS(SELECT '10.20.30.40' ip_address FROM dual UNION ALLSELECT 'a.b.c.d' ip_address FROM dual UNION ALLSELECT '256.123.0.254' ip_address FROM dual UNION ALLSELECT '255.255.255.255' ip_address FROM dual)SELECT *FROM IPWHERE REGEXP_LIKE(ip_address, '^(([0-9]{1}|[0-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])/.){3}([0-9]{1}|[0-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])$');--是否为有效身份证/手机号,暂未举例

2. SQL Server

目前最新版本为SQL Server 2017,还没有对REGEXP函数的支持,需要通用CLR来扩展,如下为CLR实现REG_REPLACE:

--1. 开启 CLR EXEC sp_configure 'show advanced options' , '1'GORECONFIGUREGOEXEC sp_configure 'clr enabled' , '1'GORECONFIGUREGOEXEC sp_configure 'show advanced options' , '0';GO
--首次创建时,应该是从dll文件创建--CREATE ASSEMBLY [RegexUtility] FROM 'C:/xxxxxxx.dll'--GO--创建好后,可以生成脚本出来部署到其他支持CLR的SQL Server上CREATE ASSEMBLY [RegexUtility]FROM 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PERMISSION_SET = SAFEGO
2. 创建 Assembly
--3. 创建 CLR 函数CREATE FUNCTION [dbo].[regex_replace](@input [nvarchar](4000), @pattern [nvarchar](4000), @replacement [nvarchar](4000))RETURNS [nvarchar](4000) WITH EXECUTE AS CALLER, RETURNS NULL ON NULL INPUTAS EXTERNAL NAME [RegexUtility].[RegexUtility].[RegexReplaceDefault]GO--4. 使用regex_replace替换多个空格为一个空格select dbo.regex_replace('agc f   f  ','/s+',' ');

注:通过CLR实现更多REGEXP函数,如果有高级语言开发能力,可以自行开发;或者直接使用一些开源贡献也行,比如:http://devnambi.com/2016/sql-server-regex/

小结:

1. 非正则SQL语句的思路,对不同数据库往往都适用;

2. 正则表达式中的规则(pattern) 在不同开发语言里,有很多语法是相通的,通常是遵守perl或者linux shell中的sed等工具的规则;

3. 从性能上来看,通用SQL判断 > REGEXP函数 > 自定义SQL函数。

参考:

http://www.oracle-developer.net/display.php?id=508

https://docs.oracle.com/cd/B12037_01/appdev.101/b10795/adfns_re.htm

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