SQL Server 类似正则表达式的字符处理问题
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
-
5. 去除所有数字/字母
一. 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1 declare @text varchar(1000) declare @str varchar(10) set @text = 'ABBBCBBBDBBBE' set @str = 'BBB' select (len(@text) - len(replace(@text,@str,'')))/len(@str) --方法2 declare @text varchar(1000) declare @str varchar(10) set @text = 'ABBBCBBBDBBBE' set @str = 'BBB' select len(replace(@text,@str,@str+'_')) - len(@text)
二. 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 Nthchar GO create 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 #T create 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 int set @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, nth from T where pos <> 0 and nth = @nth order 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 table IF 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 int SET @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 no3 from @T cross 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 SSIS FINDSTRING([yourColumn], "|", 2), --TOKEN in SQL Server 2012 SSIS TOKEN(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;
三. 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,' ',' ') end select @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”;
四. 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。
五. 去除所有数字/字母
上面定位第N个字符的方式也都可以尝试使用,只是在定位的同时将数字/字母替换掉即可;
另外也可以通过模糊匹配来做:
--去除所有非数字 declare @pos smallint declare @string varchar(100) set @string = '1109A><":{$%^&*4DSE2@!~$%^&567KJHGT' --如果是1102e53这样的字符串,会被isnumeric认为是科学计数法数字,加上e0就会返回0 --如果是普通数字,加上e0也不会影响返回1 while isnumeric(@string+'e0') = 0 --也可同下用patindex判断 begin set @pos = (select patindex('%[^0-9]%',@string)) set @string = (select replace(@string,substring(@string,@pos,1),'')) end select @string --去除所有数字 declare @pos smallint declare @string varchar(100) set @string = '1109A><":{$%^&*4DSE2@!~$%^&567KJHGT' while patindex('%[0-9]%',@string) > 0 begin set @pos = (select patindex('%[0-9]%',@string)) set @string = (select replace(@string,substring(@string,@pos,1),'')) end select @string --去除所有字母 declare @pos smallint declare @string varchar(100) set @string = '1109A><":{$%^&*4DSE2@!~$%^&567KJHGT' while patindex('%[A-Za-z]%',@string) > 0 begin set @pos = (select patindex('%[A-Za-z]%',@string)) set @string = (select replace(@string,substring(@string,@pos,1),'')) end select @string
六. 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IP WITH IP AS( SELECT '10.20.30.40' ip_address FROM dual UNION ALL SELECT 'a.b.c.d' ip_address FROM dual UNION ALL SELECT '256.123.0.254' ip_address FROM dual UNION ALL SELECT '255.255.255.255' ip_address FROM dual ) SELECT * FROM IP WHERE 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])$'); --是否为有效身份证/手机号,暂未举例
(5) 去除所有数字/字母
--去除非数字 SELECT regex_replace('1109A><":{$%^&*4DSE2@!~$%^&567KJHGT','[^0-9]','') FROM dual; --去除数字 SELECT regex_replace('1109A><":{$%^&*4DSE2@!~$%^&567KJHGT','[0-9]','') FROM dual; --去除字母 SELECT regex_replace('1109A><":{$%^&*4DSE2@!~$%^&567KJHGT','[A-Za-z]','') FROM dual;
2. SQL Server
目前最新版本为SQL Server 2017,还没有对REGEXP函数的支持,需要通用CLR来扩展,如下为CLR实现REG_REPLACE:
--1. 开启 CLR EXEC sp_configure 'show advanced options' , '1' GO RECONFIGURE GO EXEC sp_configure 'clr enabled' , '1' GO RECONFIGURE GO EXEC sp_configure 'show advanced options' , '0'; GO
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
--首次创建时,应该是从dll文件创建 --CREATE ASSEMBLY [RegexUtility] FROM 'C:\xxxxxxx.dll' --GO --创建好后,可以生成脚本出来部署到其他支持CLR的SQL Server上 CREATE ASSEMBLY [RegexUtility] FROM 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WITH PERMISSION_SET = SAFE GO
--3. 创建 CLR 函数 CREATE FUNCTION [dbo].[regex_replace](@input [nvarchar](4000), @pattern [nvarchar](4000), @replacement [nvarchar](4000)) RETURNS [nvarchar](4000) WITH EXECUTE AS CALLER, RETURNS NULL ON NULL INPUT AS EXTERNAL NAME [RegexUtility].[RegexUtility].[RegexReplaceDefault] GO
--4. 使用regex_replace替换多个空格为一个空格 select dbo.regex_replace('agc f f ','\s+',' ');
--5. 使用regex_replace去除数字/字母 --去除非数字 select dbo.regex_replace('1109A><":{$%^&*4DSE2@!~$%^&567KJHGT','[^0-9]',''); --去除数字 select dbo.regex_replace('1109A><":{$%^&*4DSE2@!~$%^&567KJHGT','[0-9]',''); --去除字母 select dbo.regex_replace('1109A><":{$%^&*4DSE2@!~$%^&567KJHGT','[A-Za-z]','');
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/
简单的正则表达式符号使用说明:
\f -> 匹配一个换页
\n -> 匹配一个换行符
\r -> 匹配一个回车符
\t -> 匹配一个制表符
\v -> 匹配一个垂直制表符
\s 匹配任何空白字符,包括空格、制表符、换页符等等, 等价于[ \f\n\r\t\v]
\s+ 匹配任意多个空白字符
\S 匹配非空白字符
^ 匹配最前边的字符
$ 与^类似,匹配最末的字符
+ 匹配+号前面的字符1次或n次.等价于{1,}
* 匹配*前面的字符0次或n次
? 匹配?前面的字符0次或1次
. (小数点)匹配除换行符外的所有单个的字符
转义字符 ESCAPE
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,非循环写法的通用SQL判断 > REGEXP函数 > 自定义SQL函数;
4. SQL SERVER 除了CLR的方式扩展正则表达式函数,也可以开启OLE Automation通过VBS来扩展正式表达式函数,曾经测试过性能,比CLR要差很多。
参考:
regular expression enhancements in 11g
http://www.oracle-developer.net/display.php?id=508
Using Regular Expressions With Oracle Database
https://docs.oracle.com/cd/B12037_01/appdev.101/b10795/adfns_re.htm
Replace non numeric characters in string
https://www.sqlservercentral.com/Forums/Topic470379-338-1.aspx
IsNumeric, IsInt, IsNumber