SQL基础操作_5_字符串处理

Posted ShenLiang2025

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目录

 

7.6 处理字符串

7.6.1 生成自增值

7.6.2 遍历字符串里的每个值

7.6.3 处理含引号的字符串

7.6.4 计算某个字符出现的次数

7.6.5 字符串里过滤不需要的字符

7.6.6 拆分字符串里的字符和数字

7.6.7 判断字符串是字符串数字型

7.6.8 判断字符串含有汉字

7.6.9 合并多行到一行

7.6.10 对字符串重新按字母排序重新组合

7.6.11 判断一个字符是否是数字

7.6.12 按照指定的位置截取字符

7.6.13 按照指定的分隔符截取字符返回表形式

7.6 处理字符串

注:数据集和表结构见 SQL基础操作_1_检索数据

7.6.1 生成自增值

需求：通过SQL生成一个1到1000条记录.

解决方法:通过CTE的递归来实现该需求.

SQLServer:

DECLARE @startINT, @endINT
SELECT @start=1, @end=1000
;WITH NumberSequence( Number) AS
(
    SELECT @start ASNumber
       UNION ALL
    SELECT Number + 1
       FROM NumberSequence
       WHERE Number <@end
)
SELECT * FROM NumberSequence OPTION (MaxRecursion 1000)

执行结果:

Number

1

2

3

...

 

Oracle:

WITH t(num) AS (
  SELECT 1 FROM DUAL
  UNION ALL
  SELECT t.num+1
  FROM t WHERE t.num<100
  )
SELECT * FROM t;

执行结果:

Num

1

2

3

...

 

Mysql(8.0及以上版本):

WITH RECURSIVE cte (num) AS
(
  SELECT 1
  UNION ALL
  SELECT num+1 FROM cte WHERE num <100
)
SELECT * FROM cte;

执行结果:

Num

1

2

3

 

…

 

7.6.2 遍历字符串里的每个值

需求：打印出ename为’King’的名字里每一个字母,每个字母占一行.

解决方法:通过自增表和emp表先cross join(笛卡尔积),然后再通过ename的len(ename的长度)进行过滤,最终得到显示每个字母的结果.

SQLServer:

SELECT SUBSTRING (e.ENAME,seq.pos,1) AS ename_Split
FROM (SELECT ENAME FROM emp WHERE ename= 'KING' ) e,
(SELECT number AS pos FROM master.[dbo].[spt_values] WHERE type = 'P' AND number>0)seq
WHERE seq.pos <= LEN(e.ename)

执行结果:

ename_Split

K

I

N

G

注:

1: 这里master.[dbo].[spt_values]是一张特殊的系统视图,里面存了从0到2047总2048条自增序列.

2: 如果不明白,可以分段来看.

Step1:

SELECT e.*,seq.* FROM
(SELECT ENAME FROM emp WHERE ename= 'KING' ) e,
(SELECT number AS pos FROM master.[dbo].[spt_values] WHERE type = 'P' AND number>0)seq

执行结果:

ENAME

pos

KING

1

KING

2

KING

3

 

 

…

…

Sept2:

SELECT SUBSTRING(e.ENAME,seq.pos,1)AS ename_Split
FROM .. e, ..seq
WHERE seq.pos<=LEN(e.ename)

这里通过SUBSTRNG函数,每次的开始位置不断调整,每次仅取一个字符,再通过LEN函数过滤.所以得到最终结果.如果不熟悉SUBSTRING的语法,这里简单介绍下.

SUBSTRING ( expression, start, length )

1) 参数expression是要截取的原始字符串,比如这里的” KING”

2) 参数start是要截取的位置,比如从第2个位置开始,那应该从” I”往后数.

3) 参数length是要截取的长度,沿用上一行的例子,如果长度定义为2,则最终截取字符串是”IN”

Oracle:

WITH t(num) AS (
  SELECT 1 FROM DUAL
  UNION ALL
  SELECT t.num+1
  FROM t WHEREt.num<100
  )
SELECT SUBSTR(e.ENAME,seq.num,1) AS ename_Split FROM
(SELECT ENAME FROM emp WHERE ename ='KING' ) e,
(SELECT num FROM t)seq
WHERE seq.num <= LENGTH(e.ename)

 Mysql 8.0:

WITH RECURSIVE cte (num)AS
(
  SELECT 1
  UNION ALL
  SELECT num+1 FROM cte WHERE num <100
)
SELECT SUBSTRING(e.ENAME,seq.num,1) AS ename_Split FROM
(SELECT ENAME FROM emp WHERE ename ='KING' ) e,
(SELECT num FROM cte)seq
WHERE seq.num <= LENGTH(e.ename)

 

7.6.3 处理含引号的字符串

需求：往dept表里插入dname为Test’s,loc为Beijing,deptno为100的数据.

解决方法:这里有位引号是特殊符号,所以需要特殊处理,比如如果双引号包裹起来.

Mysql:

INSERT INTO dept VALUES(100,'Test\\'s','Beijing');

Sql Server:

BEGIN TRAN
   SET IDENTITY_INSERTdeptON;
   GO
   INSERT INTO dept(deptno,dname,loc) VALUES (100,'Test''s','Beijing');
   SELECT * FROM dept WHERE deptno=100;
   SET IDENTITY_INSERTdeptOFF;
   GO
ROLLBACK TRAN

执行结果:

deptno

dname

loc

100

Test's

Beijing

 

7.6.4 计算某个字符出现的次数

需求：查询emp表emptno是7499的用户的job里S出现的次数.

解决方法:这里length(len)结合replace函数算出字符串出现的次数.

Sql Server:

SELECT empno,job,(LEN(JOB) - LEN(REPLACE(JOB,'S','')))/LEN('S') AS StrFreq
FROM emp WHERE empno=7499;

empno

job

StrFreq

7499

SALESMAN

2

Mysql:

SELECT empno,job,ROUND((LENGTH(JOB) - LENGTH(REPLACE(JOB,'S','')))/LENGTH('S')) AS StrFreq
FROM emp WHERE empno=7499;

注:这里除以LENGTH('S')是为了考虑传入的字符串是2位以及以上的情况,比如’SS’.

 

7.6.5 字符串里过滤不需要的字符

需求：过滤tmp_v视图里含数字的部分. 其中tmp_v视图的data字段的定义是emp表的ename字段拼接空格和deptno字段。

解决方法:这里通过translate函数对含数字的部分进行替换.

SQL Server:

create view tmp_v
AS SELECT ename+' '+cast(deptno as varchar)as data
from emp

SELECT data,replace(dbo.translate(data,'0123456789','@@@@@@@@@@'),'@','') as ename FROM tmp_v
order by replace(dbo.translate(data,'0123456789','@@@@@@@@@@'),'@','') desc

data

ename

WARD 30

WARD

TURNER 30

TURNER

SMITH 20

SMITH

SCOTT 20

SCOTT

MILLER 10

MILLER

MARTIN 30

MARTIN

KING 10

KING

JONES 20

JONES

JAMES 30

JAMES

FORD 20

FORD

CLARK 10

CLARK

BLAKE 30

BLAKE

ALLEN 30

ALLEN

ADAMS 20

ADAMS

注：这里需要参考之前章节里translate函数的实现.

Mysql：

create view tmp_v
AS SELECT CONCAT(ename,' ',deptno) as data
from emp
SELECT data,replace(translate(data,'0123456789','@@@@@@@@@@'),'@','') as ename
FROM tmp_v
order by replace(translate(data,'0123456789','@@@@@@@@@@'),'@','') desc

Oracle：

 

7.6.6 拆分字符串里的字符和数字

需求：过滤tmp_v视图里data字段拆分会原来的ename和deptno两个字段.

解决方法:这里通过translate、replace、repeate（replicate、rpad）函数对含数字的部分进行替换.

SQL Server：

SELECT data,replace(dbo.translate(data,'0123456789',REPLICATE('@',10)),'@','') as ename,
replace(dbo.translate(data,'ABCDEFGHIJKLMNOPQRSTUVWXYZ',REPLICATE('@',26)),'@','') as deptno
FROM tmp_v
order by replace(dbo.translate(data,'0123456789',REPLICATE('@',10)),'@','') desc

data

ename

deptno

WARD 30

WARD

 30

TURNER 30

TURNER

 30

SMITH 20

SMITH

 20

SCOTT 20

SCOTT

 20

MILLER 10

MILLER

 10

MARTIN 30

MARTIN

 30

KING 10

KING

 10

JONES 20

JONES

 20

JAMES 30

JAMES

 30

FORD 20

FORD

 20

CLARK 10

CLARK

 10

BLAKE 30

BLAKE

 30

ALLEN 30

ALLEN

 30

ADAMS 20

ADAMS

 20

Mysql:

SELECT data,replace(translate(data,'0123456789',REPEAT('@',10)),'@','') as ename,
replace(translate(data,'ABCDEFGHIJKLMNOPQRSTUVWXYZ',REPEAT('@',26)),'@','') as deptno
FROM tmp_v
order by replace(translate(data,'0123456789',REPEAT('@',10)),'@','') desc

 

 

7.6.7 判断字符串是字符串数字型

需求：检索temp_strdata表的字段data是字符串数字类型的记录这里如果都是字符串或者数字的也符合条件.

解决方法:这里通过translate、replace、repeate（replicate、rpad）函数对含数字的部分进行替换.

SqlServer：

CREATE TABLE temp_str(data VARCHAR(1000));
INSERT INTO temp_str VALUES('SMITH20');
INSERT INTO temp_str VALUES('JONES30');
INSERT INTO temp_str VALUES('Jim#40');
INSERT INTO temp_str VALUES('50$Tom');
INSERT INTO temp_str VALUES('60:Mike');
INSERT INTO temp_str VALUES('70Cruz');
INSERT INTO temp_str VALUES('Jack');
INSERT INTO temp_str VALUES('J8oh0n');

SELECT data --,dbo.translate(UPPER(data),'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',REPLICATE('a',36)) as trans
FROM temp_str
WHERE dbo.translate(UPPER(data),'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',REPLICATE('a',36))=REPLICATE('a',LEN(data))
 

7.6.8 判断字符串含有汉字

需求：检索含有汉字的字符串.

解决方法:这里通过函数CHAR_LENGTH对比LENGTH进行对比来判断.

Mysql:

SELECT data,LENGTH(data) AS Len_data,CHAR_LENGTH(data) AS CharLen_Data,HEX(data) AS HexData FROM
(
SELECT 'Hello,World,SQL'AS data
    UNION ALL
SELECT 'Data,Arithmetic' AS data
    UNION ALL
SELECT 'Science中国' AS data
    UNION ALL
SELECT '上S海H' AS data   
)A
WHERE LENGTH(data) <> CHAR_LENGTH(data)

执行结果:

data

Len_data

CharLen_Data

Science中国

13

9

上S海H

8

4

注:

LENGTH() returnsthe length of the string measured in bytes. 
CHAR_LENGTH() returns the length of the string measured incharacters.

LENGTH:是计算字节的长度.一个汉字是算三个字符,一个数字或字母算一个字符

CHAR_LENGTH:汉字、数字、字母都算是一个字符

或者通过字符串的十六进制并结合REGEXP来判断.

SELECT data,HEX(data) AS HexData FROM
(
SELECT 'Hello,World,SQL' AS data
    UNION ALL
SELECT 'Data,Arithmetic'AS data
    UNION ALL
SELECT 'Science中国' AS data
    UNION ALL
SELECT '上S海H' AS data   
)A
WHERE HEX(data) REGEXP'^(..)*(E[4-9])'

执行结果:

data

HexData

Science中国

536369656E6365E4B8ADE59BBD

上S海H

E4B88A53E6B5B748

SQL Server:

SELECT data FROM
(
SELECT  'Hello,World,SQL' AS data
    UNION ALL
SELECT  'Data,Arithmetic' AS data
    UNION ALL
SELECT  'Science中国' AS data
    UNION ALL
SELECT  '上S海H' AS data   
)A
WHERE data LIKE  '%[吖-座]%'

 

-- 或者利用PATINDEX函数进行判断
SELECT data  FROM
( SELECT 'Hello,World,SQL' AS data
    UNION ALL
SELECT 'Data,Arithmetic' AS data
    UNION ALL
SELECT 'Science中国' AS data
    UNION ALL
SELECT '上S海H' AS data  
)A
WHERE PATINDEX ('%[吖-座]%',data) > 0

执行结果:

data

Science中国

上S海H

 

7.6.9 合并多行到一行

需求：将emp表里deptno相同的ename以逗号拼接在一起.

解决方法:这里通过字符串合并函数完成该效果.如group_concat

SQL Server:

SELECT DISTINCT
     deptno
    , STUFF((
       SELECT N', '+ CAST([ename]ASVARCHAR(255))
       FROM emp e1
       WHERE e1.deptno= e2.deptno
       FOR XML PATH ('')), 1, 2,'')AS StrCombine
FROM emp e2

执行结果:

Deptno

StrCombine

10

CLARK, KING, MILLER

20

SMITH, JONES, SCOTT, ADAMS, FORD

30

ALLEN, WARD, MARTIN, BLAKE, TURNER, JAMES

或者借助CTE:

WITH x(deptno,cnt,list,empno,len)
AS(
SELECT deptno,COUNT(*) OVER(PARTITIONBY deptno),CAST(ename AS VARCHAR(100)),empno,1
FROM emp
UNION ALL
SELECT x.deptno,x.cnt,CAST(x.list+','+e.ename AS VARCHAR(100)),e.empno,x.len+1
FROM emp e,x
WHERE e.deptno= x.deptno
AND e.empno> x.empno
)
SELECT deptno,list AS StrCombine from X
WHERE len=cnt
ORDER BY 1

步骤分析:

Step1: 首先借助COUNT(*) OVER(PARTITION BY deptno)确定每个部门里有多少员工

Step2: 借助len,初始值为1,完成自增(递归里 x.len+1)

Step3: 借助x.list+','+e.ename完成ename的拼接

Step4: 借助e.deptno = x.deptno AND e.empno >x.empno确定要递归的结果集

Step5: 查询满足条件的记录,即按deptno分组的empno数和自增序号相同的记录.

分步查看结果:

1)  查看构建的递归数据.这里以depto=10的为例:

SELECT * FROM x WHERE deptno= 10

deptno

cnt

list

empno

len

10

3

CLARK

7782

1

10

3

KING

7839

1

10

3

MILLER

7934

1

10

3

KING,MILLER

7934

2

10

3

CLARK,KING

7839

2

10

3

CLARK,MILLER

7934

2

10

3

CLARK,KING,MILLER

7934

3

2)  不难发现,这里高亮处的数据是我们想要的,所以通过如下方式获取最终结果:

SELECT deptno,list AS StrCombine FROM X
WHERE len=cnt
ORDER BY 1

延展阅读:如果仅想获得某一个分组下的字符串合并,也可以按照如下方法:

DECLARE @combinedString VARCHAR(MAX)
SELECT @combinedString = COALESCE(@combinedString+', ','')+ ename
FROM emp
WHERE deptno=10
SELECT @combinedString as StringValue

Mysql:

SELECT deptno,group_concat(ename) AS StrCombine FROM emp
GROUP BY deptno
ORDER BY emp.deptno,ename

 

7.6.10 对字符串重新按字母排序重新组合

需求：将emp表里ename按照字母顺序重新组合生成新的字符.

解决方法:这里通过字符串合并函数或者结合substring和row_number完成该效果.

SqlServer:

WITH x(ename,ename_Split) AS
(
SELECT TOP 100000 ename,SUBSTRING(e.ENAME,seq.pos,1) AS ename_Split
           FROM (SELECT ENAME FROM emp) e,
           (SELECT number AS pos FROM master.[dbo].[spt_values] WHERE type= 'P' AND number>0) seq
           WHERE seq.pos <= LEN(e.ename)
           ORDER BY ename, ename_Split

)
 SELECT DISTINCT
     ename
    , STUFF((
       SELECT N''+ CAST(ename_SplitASVARCHAR(255))
       FROM x e1
       WHERE e1.ename= e2.ename
       FOR XML PATH ('')),1,0,'')AS StrByAlph
FROM x e2

注: 如果想在CTE里使用[]排序,需要在查询里指定TOP.

消息 1033，级别 15，状态 1，第 67 行

除非另外还指定了 TOP、OFFSET 或 FORXML，否则，ORDER BY 子句在视图、内联函数、派生表、子查询和公用表表达式中无效。

执行结果:

ename

StrByAlph

ADAMS

AADMS

ALLEN

AELLN

BLAKE

ABEKL

CLARK

ACKLR

FORD

DFOR

JAMES

AEJMS

JONES

EJNOS

KING

GIKN

MARTIN

AIMNRT

MILLER

EILLMR

SCOTT

COSTT

SMITH

HIMST

TURNER

ENRRTU

WARD

ADRW

 

 

 

Mysql:

SELECT ename,group_concat(SUBSTRING(e.ENAME,seq.num,1) ORDER BY SUBSTRING(e.ENAME,seq.num,1) separator '') AS StrByAlph
FROM (SELECT ENAME FROM emp) e,
    (SELECT i AS num FROM tb_incr)seq
WHERE seq.num <= LENGTH(e.ename)
GROUP BY ename
ORDER BY ename,SUBSTRING(e.ENAME,seq.num,1)

 

注: 这里借助group_concat函数里的ORDER BY关键字,对已经排序的字母进行合并.

这里tb_incr是个自增表,存放从1开始步长为1的自增序列

Oracle:

 

7.6.11 判断一个字符是否是数字

需求：将临时表里判断data字段里哪些是数字.

解决方法:这里通过函数isnumberic或者regexp完成该效果.

Mysql:

DELIMITER $$
DROP FUNCTION IF EXISTS `IsNum` $$
CREATE FUNCTION `IsNum`(str VARCHAR(25)) RETURNS INT
BEGIN
    DECLARE iResult INT DEFAULT 0;
    IF ISNULL(str) THEN return 0;END IF;-- NULL 字符串
    IF str='' THEN return 0;END IF;-- 空字符串
    SELECT str REGEXP '^[0-9]*$' INTO iResult;
    IF iResult =1 THEN
       RETURN 1;
    ELSE
       RETURN 0;
    END IF;
    END $$
DELIMITER ;

或者使用正则表达式:

SELECT data FROM
(
SELECT '63' AS data
UNION ALL
SELECT '36(' AS data
UNION ALL
SELECT '3(6' AS data
UNION ALL
SELECT '(36' AS data
UNION ALL
SELECT '36$' AS data
UNION ALL
SELECT '' AS data
UNION ALL
SELECT NULL AS data
)A
-- WHERE IsNum(data) = 1
WHERE data REGEXP '^[0-9]*$'=1 AND data IS NOT NULL AND data<> '';

或者直接通过函数IsNum(data) = 1来判断,见注释部分.

SqlServer:

SELECT data FROM
(
SELECT '63' AS data
UNION ALL
SELECT '36(' AS data
UNION ALL
SELECT '3(6' AS data
UNION ALL
SELECT '(36' AS data
UNION ALL
SELECT '36$'AS data
UNION ALL
SELECT  '' AS data
UNION ALL
SELECT NULL AS data
)A
WHERE ISNUMERIC(data)= 1

执行结果:

Data

63

 

7.6.12 按照指定的位置截取字符

需求：按照逗号拆分字符串,取拆分出来的第二个子串.

解决方法:这里需要自定义函数结合substring截取字符串,以达到该效果.

SQL Server:

CREATE FUNCTION strSplitIndex 
( @str VARCHAR(1024), --要分割的字符串
 @split VARCHAR(10), --分隔符
 @index INT --要取元素的位置
) 
RETURNS VARCHAR(1024) 
AS 
BEGIN 
  DECLARE @location INT 
  DECLARE @start INT 
  DECLARE @next INT 
  DECLARE @seed INT 
  SET @str=LTRIM(RTRIM(@str)) 
  SET @start=1 
  SET @next=1 
  SET @seed=LEN(@split) 
  SET @location=CHARINDEX(@split,@str) 
  WHILE @location<>0and @index>@next 
  BEGIN 
    SET @start=@location+@seed 
    SET @location=CHARINDEX(@split,@str,@start) 
    SET @next=@next+1 
  END 
  IF @location =0 SELECT @location =LEN(@str)+1 
  RETURN SUBSTRING(@str,@start,@location-@start) 
END
GO
SELECT dbo.strSplitIndex(data,',',1) AS StrSplit FROM
(
   SELECT 'Hello,World,SQL' AS data
   UNION ALL
   SELECT 'Data,Arithmetic' AS data
   UNION ALL
   SELECT  'Science' AS data
 )A

执行结果:

StrSplit

Hello

Data

Science

或者借助parsename函数:

SELECT PARSENAME(REPLACE(data,',','.'),2) AS StrSplit FROM
(

SELECT  'Hello,World,SQL' AS data
   UNION ALL
   SELECT  'Data,Arithmetic' AS data
   UNION ALL
   SELECT  'Science' AS data
)A
WHERE PARSENAME(REPLACE(data,',','.'),2)IS NOT NULL

执行结果:

StrSplit

Hello

Data

Mysql:

SELECT data,SUBSTRING_INDEX(SUBSTRING_INDEX(data,',',seq.num),',',-1) AS sub,seq.num AS subStrPos
FROM
(SELECT 'Hello,World,SQL' AS data
    UNION ALL
SELECT 'Data,Arithmetic' AS data
    UNION ALL
SELECT 'Science' AS data) e,
(SELECT ias num FROM tb_incr)seq
WHERE seq.num <= LENGTH(e.data)- LENGTH(REPLACE(e.data,',',''))+1
AND seq.num=2
ORDER BY data,seq.num

执行结果:

data

sub

subStrPos

Data,Arithmetic

Arithmetic

2

Hello,World,SQL

World

2

步骤解析:

Step1: 首先借助自增表将data字段里的数据按照逗号的数目切分,如果有2个逗号,则会切分成3部分

Step2: 借助SUBSTRING_INDEX函数截取逗号所在位置的子串,这里鉴于SUBSTRING_INDEX的第三个参数的意义是子串累加,所以又套了个SUBSTRING_INDEX,第三个参数传-1,即从右边截取.

Step3:借助自增表的num,取指定分割位置的数据,这里是2.

注: SUBSTRING_INDEX函数执行示例见下:

SELECT SUBSTRING_INDEX('Hello,World,SQL',',',1) AS SUBSTRING,1 AS pos
UNION ALL
SELECT SUBSTRING_INDEX('Hello,World,SQL',',',2) AS SUBSTRING,2 AS pos
UNION ALL
SELECT SUBSTRING_INDEX('Hello,World,SQL',',',3) AS SUBSTRING,3 AS pos

执行结果:

SUBSTRING

pos

Hello

1

Hello,World

2

Hello,World,SQL

3

 

Oracle:

 

7.6.13 按照指定的分隔符截取字符返回表形式

需求：按照逗号拆分字符串,并指定返回的格式是表.

解决方法:这里需要自定义函数结合substring截取字符串,以达到该效果.

SQLServer:

CREATE FUNCTION strSplitTable(@strNVARCHAR(2000),@splitNVARCHAR(2))
RETURNS @t TABLE(SubStr VARCHAR(1000))
AS
BEGIN
DECLARE @tmpSubStr VARCHAR(1000),@getIndexINT
SET  @getIndex=CHARINDEX(',',@str)
WHILE(@getIndex<>0)  
BEGIN
    SET @tmpSubStr=CONVERT(VARCHAR(1000),SUBSTRING(@str,1,@getIndex-1))
    INSERT INTO @t(SubStr)VALUES(@tmpSubStr)
    SET @str=STUFF(@str,1,@getIndex,'')
    SET  @getIndex=CHARINDEX(',',@str)  
END
INSERT INTO @t(SubStr)VALUES(@str)
RETURN
END
GO
SELECT * FROM strSplitTable('Hello,World,SQL',',')

执行结果:

SubStr

Hello

World

SQL

注:  自Sql Server 2016已新增系统函数STRING_SPLIT,测试示例见下:

SELECT A.value value_A,B.value value_B 
FROM 
( SELECT value FROM STRING_SPLIT('A$B$C','$') 
)A
LEFT JOIN 
(SELECT value FROM STRING_SPLIT('A,B',',') 
)B
ON A.value = B.value

执行结果:

value_A

value_B

A

A

B

B

C

NULL

这里仅支持单个字符的分隔符.

消息 214，级别 16，状态 11，第 12 行
Procedure expects parameter 'separator' of type 'nchar(1)/nvarchar(1)'.

Mysql:

未见该方法.

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