General Notes




This "workbench" on string handling and manipulation in SQL Server is

a companion to my previous one on dates and times. Rather than rehash

what is readily available on SQL Server Books on Line, I've once

again tried to provide a a starting point for your own experiments.

It is structured so it can be pasted in its entirety into the Query

Analyser, SSMS or other GUI and the individual examples executed (and

it is available, zipped up, as an attachment to the article).

The main difficulty in dealing with Strings in SQL Server is that the

techniques are rather open-ended. There are often a number of

different ways to achieve the same end result. The String functions

such as STUFF or REVERSE are of little use by themselves, but when

used in conjunction with others, they become extremely useful. Other

functions are there as 'legacy items' meaning that it is difficult

to remove functions such as SOUNDEX as there are still a few die-

hards still using them

As with the previous 'workbench', my advice is to download the .sql

file (see the Code Download link to the right of the article title)

open it up in SQL Server, and start experimenting!

Ideally, you'll also have Books online open in a browser, to provide

supplementary and background information.

I've added a few questions at the end just so you can check on your

progress. Overall, I hope that this workbench illustrates how easy

string handling is in SQL Server once the basic ideas are grasped.



Selecting from a table

The String Datatypes

Strings and Collations

Assignment and truncation

The String Functions


       ASCII and UNICODE










       removing leading or trailing spaces RTRIM & LTRIM

       Changing Case UPPER and LOWER

       Fuzzy searches,  SOUNDEX and DIFFERENCE

Manipulating TEXT and NTEXT

Some Questions


As a practice table for this workbench we will create a temporary

table and stock it with string data.


CREATE TABLE #Poem (line VARCHAR(255), theOrder INT IDENTITY(1,1))

INSERT INTO #poem(line)

       SELECT 'I will pen me my memoirs.'

INSERT INTO #poem(line)

       SELECT 'Ah, youth, youth! What euphorian days them was!'

INSERT INTO #poem(line)

       SELECT 'I wasn''t much of a hand for the boudoirs,'

INSERT INTO #poem(line)

       SELECT 'I was generally to be found where the food was.'

INSERT INTO #poem(line)

       SELECT 'Does anybody want any flotsam?'

INSERT INTO #poem(line)

       SELECT 'I''ve gotsam.'

INSERT INTO #poem(line)

       SELECT 'Does anybody want any jetsam?'

INSERT INTO #poem(line)

       SELECT 'I can getsam.'

INSERT INTO #poem(line)

       SELECT 'I can play ''Chopsticks'' on the Wurlitzer,'

INSERT INTO #poem(line)

       SELECT 'I can speak Portuguese like a Berlitzer.'

/*from Odgen Nash's wonderful poem 'No Doctors Today, Thank-you'

Note the way that one inserts the ' delimiter (as in "I can play

'Chopsticks' on the Wurlitzer") by putting in a second ' character

SQL Server inherits from its Sybase ancestry a limit to the size of

string. This complicates the manipulation of large quantities of

text. However, this limit has been remedied in SQL Server 2005 with

the special datatype, Varchar(MAX). TEXT is now deprecated as a

datatype but is used sufficiently in versions previous to SQL Server

2005 to make it relevant.

Selecting from a table



--you can, of course, select according to strings, or partial strings

SELECT line FROM #poem WHERE line LIKE 'I Was%'--'I Was' at

--the start of the line ('%' means 'any number 0-n of any character)

SELECT line FROM #poem WHERE line LIKE '%sam%'--'sam' anywhere

SELECT line FROM #poem WHERE line LIKE '%?%'--? anywhere

SELECT line FROM #poem WHERE line BETWEEN 'a' AND 'e'--returns

--all lines starting with a,b,c or d

SELECT line FROM #poem WHERE line < 'D' --returns one line

SELECT line FROM #poem WHERE ' '+line LIKE '% g_tsam%'

--here we want only words starting with g?tsam. the underscore

--character means 'one character, anything you like'. The leading

--space makes the logic simpler as it allows for occurences of the

--word at the beginning of the line

SELECT line FROM #poem WHERE ' '+line LIKE '%[aeiou][aeiou]%'

--any line with two consecutive vowels in it

--the '[]' delimiters contain a range of characters

--and mean 'one character, anything in the range'

--here, it is a list of vowels

SELECT line FROM #poem WHERE ' '+line LIKE '%[^a-z][aeiou][aeiou]%'

-- returns any line containing a word beginning with two vowels

--the [^a-z] will mean a whitespace character in European

--languages as long as you set your collation accordingly!


The String Datatypes


There are three basic string types (Unicode equivalents shown in


       Char (nChar)

       Varchar (nVarchar)

       Text (nText)

The nearest equivalents between the new 2005 string variables and

previous versions is as follows:

       XML -> nText

       Varchar(MAX) -> Text

       nVarchar(MAX) -> nText

(If replicating from a SQL Server 2005 publisher to a SQL Server 2000

subscriber, this mapping is done automatically but it's well to be

aware of what is going on).

Most European languages can be represented by the eight-bit character

sets. For a 'global' system that can represent all languages, one

must opt for Unicode, and use NVarchar, or NChar or NText.

Peculiarly, the method of representing Unicode constants is case-

sensitive, being the uppercase N prefix (N stands for National

Language in the SQL-92 standard)*/

SELECT '˜˜˜',N'˜˜˜' --???       ˜˜˜

--in the first case the characters cannot be represented (musical

--notes, but in the second case, they can

/*Unicode constants are interpreted as Unicode data, and are not

evaluated using a code page. Unicode constants do have a collation,

though, which determines comparisons and case sensitivity. Unicode

data is stored using two bytes per character         */

SELECT DATALENGTH(N'This one is a unicode string'),

        DATALENGTH('This is not a unicode string')

/* ----------- -----------

   56          28
You'll see that the first string needed twice the storage of the

second Unicode string constants support enhanced collations.

Strings and Collations


Collations determine the result of sorts, and string comparisons.

Constants are assigned the default collation of the current database,

unless the COLLATE clause is used to override it.

to see what are available, use...      */

SELECT * FROM ::fn_helpcollations()

/*... which produces a list of many collations, including the

following ...






...which you can then try them out in these expressions*/

SELECT CASE WHEN 'A'<>'a' collate Latin1_General_CI_AI

               THEN 'Different' ELSE 'same' END

-- same

SELECT CASE WHEN 'A'<>'a' collate Latin1_General_CS_AI

               THEN 'Different' ELSE 'same' END

-- different


So any function or stored procedure that is intended to be portable

across databases must be explicit about collation where necessary.

Collations can be selected at Server, Database, column or expression,

but we'll only illustrate its selection in an expression.*/


Some of the jargon and abbreviations used in the names for the

collations require explanation

Binary BIN

       Binary is the fastest sorting order. It sorts and compares

       data based on the bit patterns defined for each character.

       Binary sort order is case-sensitive (lowercase precedes

       uppercase), and accent-sensitive.

       If one chooses a language-based sort rather than a binary

       sort, SQL Server follows sorting and comparison rules as

       defined in dictionaries for the associated language or


Case-sensitive CS

       Case-sensitive collation means that the uppercase and

       lowercase versions of letters are considered different.


       SELECT CASE WHEN 'A'<>'a' collate Latin1_General_CS_AI

                               THEN 'Different' ELSE 'same' END


Accent-sensitive AS

       Accent-Sensitive collation means that, For example,

       'a' is not equal to '¨¢'. and will sort strings so that

       strings beginning with a but with different accents, will

       not be sorted together*/

       SELECT CASE WHEN 'a'<>'¨¢' collate Latin1_General_CI_AS

                               THEN 'Different' ELSE 'same' END


Kana-sensitive KS

       specifies that the two types of Japanese kana characters:

       Hiragana and Katakana, are different

Width-sensitive WS

       specifies that a single-byte (half-width) 'hankaku' character

       and the same character represented as a double-byte

       (full-width)  ¡°zenkaku¡± character are different Half-width

       characters has a glyph image that occupies half of the

       character display cell.

Assignment and Truncation


String variables work similarly to string data in tables except for

the way SQL Server behaves if an attempt is made to assign a string

that is longer than the variable's length.

One has to be very careful to watch out for truncation when assigning

to string variables. Assigning to a string variable causes truncation

without causing an error. This is done in order to achieve

consistency with the behaviour of the CHAR datatype. */

DECLARE @message VARCHAR(20)

SELECT @Message=

 'This is a long string which will get truncated without you knowing'

SELECT @Message


--      This is a long strin

--..whereas inserting into a table triggers an error

DECLARE @messageTable TABLE (message VARCHAR(20))

INSERT INTO @MessageTable(Message)

       SELECT 'This is a very long long string which will overflow'


--      String or binary data would be truncated.

--      The statement has been terminated.

--if you are passing a variable to a stored procedure or function,

--again it truncates without telling you!

CREATE PROCEDURE #spTestStringParameter

@message VARCHAR(20)


SELECT @message


EXECUTE #spTestStringParameter

      'This is a string which will get truncated without you knowing'

So, where necessary, it is wise to check the string inputs for

possible overflow. Here is a fragment of a stored procedure that

checks for overflow. I've been caught out many times so I advise

you to put in a precaution like this   */

ALTER PROCEDURE #spTestStringParameter

@message VARCHAR(21)


IF LEN(@message)=21


       'input parameter @message, beginning ''%s...'' truncated!',


SELECT @message



The string Functions




the LEN function returns the length of the string

Finding the length of a string is not always straightforward.*/

SELECT LEN('Who would have thought this was shorter            ')--39

SELECT LEN('                                       ...than this')--51

/*...because the length of strings in SQL Server do not include

trailing spaces this means that, if you want the true length of a

string it must be done by   */


       'This string has trailing spaces              ',' ','|'))--45



       'This string has trailing spaces              '+'.')-1--45

/* in the first example, we substitute a different character for the

space (it doesn't matter what), whereas, in the second case we add a

non-space character so the spaces aren't trailing

         ASCII and UNICODE


The ASCII function returns the ASCII code of the first character of a

char or Varchar string it returns the ASCII value of ? if it can't do

so! */


/* so let's use a simple bit of code, illustrating the use of ASCII,

to display the character values of the characters in a string, (I've

 used this in an emergency in the past)*/


DECLARE @originalString VARCHAR(80)

SELECT @originalString='        What

is here?'

WHILE LEN(@originalString)>0


       SELECT @ASCIIValues=COALESCE(@ASCIIValues+',','')

                       +CAST(ASCII(@OriginalString) AS VARCHAR)

       SELECT @originalString=SUBSTRING(@originalString,2,80)


SELECT @AsciiValues




UNICODE does the same thing for a Unicode string that ASCII does for




This will give you the character represented by the Unicode. Note
how one can represent character values as hex strings. Here, to

illustrate its use, are some useful Unicode currency symbols!*/

SELECT NCHAR(0x20AB),'Vietnamese Dong'

SELECT NCHAR(0x20AA),'Shequel'

SELECT NCHAR(0xA3),'pound sign'

SELECT NCHAR(0x20A3),'French Franc'

SELECT NCHAR(0x20Ac),'Euro'

SELECT NCHAR(0x20A8),'Rupee'

SELECT NCHAR(0x20A7),'Peseta'

SELECT NCHAR(0x20A6),'Naira'

/*You may need to set your results pane to Unicode to see these




returns the ASCII character represented by the integer code.

In this example we’ll put a CR/Linefeed sequence into a string */

SELECT 'first line'+CHAR(13)+CHAR(10)+ 'second line'


-- first line

-- second line




PATINDEX provides you with a great deal of versatility in

finding strings in TEXT data. It also allows you to search

by wildcard.

We could, for example, show the part of the string with the first

occurrence of a word that starts with two or more vowels*/

SELECT '...'+SUBSTRING(line,PATINDEX('% [aeiou][aeiou]%',line),10)


       FROM #poem

       WHERE ' '+line LIKE '% [aeiou][aeiou]%'

/* the usefulness of patindex is fundamentally lessened by the fact

that there is no way of detecting the end of the sequence in the

original string that matched the wildcard. */




Charindex provides a standard way of searching within strings to find

a substring, and returning the starting position of the string.

It has the added versatility of allowing you to specify the starting

location of the search. This is especially useful in places where

you must find all occurrences of a string. Consider the following

simple routine which splits delimited strings (such as you might find

in 'serialised' data) into a table.



CREATE   FUNCTION dbo.uftSplitVarcharToTable


@StringArray VARCHAR(8000),

@Delimiter VARCHAR(10)



@Results TABLE


SeqNo INT IDENTITY(1, 1), Item VARCHAR(8000)





DECLARE @lenStringArray INT

DECLARE @lenDelimiter INT


--initialise everything

SELECT @ii=1, @lenStringArray=LEN(REPLACE(@StringArray,' ','|')),

@lenDelimiter=LEN(REPLACE(@Delimiter,' ','|'))

--notice we have to be cautious about LEN with trailing spaces!

--while there is more of the string…

WHILE @ii<=@lenStringArray

BEGIN--find the next occurrence of the delimiter in the stringarray

SELECT @next=CHARINDEX(@Delimiter,  @StringArray + @Delimiter, @ii)

INSERT INTO @Results (Item)

       SELECT SUBSTRING(@StringArray, @ii, @Next - @ii)

--note that we can get all the items from the list by appeending a

--delimiter to the final string

SELECT @ii=@Next+@lenDelimiter





--and the routine can be used simply like this...

SELECT * FROM dbo.uftSplitVarcharToTable(



you should see all the items from the list in a table.

Once you have a function like this, you can then use it for such

esoteric tasks as, for example, stripping tags out of HTML or XML!


DECLARE @HTMLString VARCHAR(8000),@Stripped VARCHAR(8000)

'<?xml version="1.0" encoding="us-ascii"?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"


<html xmlns="">





    <div style="float left: width:300px;">

      <p style="font-size:larger">

        <strong><em>Song of the Open Road</em></strong>


      I think that I shall never see<br />

      A billboard Lovely as a tree<br />

      Perhaps unless the billboards fall,<br />

'll never see a tree at all<br />




SELECT @Stripped = COALESCE(@Stripped,'')

       + thetext FROM


          [thetext]=SUBSTRING(Item, CHARINDEX('>', Item) + 1, 8000),


          FROM dbo.uftSplitVarcharToTable(@HTMLString, '<'))f

WHERE theText <>CHAR(13)+CHAR(10)


SELECT @Stripped

/*    which will yield the following poem....

Song of the Open Road

      I think that I shall never see

      A billboard lovely as a tree

      Perhaps unless the billboards fall,

      I'll never see a tree at all 

Naturally, the technique works just as easily stripping bracketed

text from strings or any other delimiter!

So with just three of the built-in functions used in a user-defined

function, you have a powerful tool



We have seen the REPLACE function being used already a a work-around

for LEN’s quirks. It is one of the most useful of the String

functions. It'll replace all occurrences of one string with another.

For example…*/


'Dear %1, you are considerably overdrawn to the tune of %2

in your %3 account.

Please phone our %4 for suggestions on debt management.'

,'%1','Miss Page'),'%2','£345.67'),'%3','current'),'%4','Mr Gross')


which will give...

Dear Miss Page, you are considerably overdrawn to the tune of £345.67

in your current account.

Please phone our Mr Gross for suggestions on debt management.








                                                       ' '+line+' ',

                                       ' was ',' were '),

                               ' wasn''t',' weren''t'),

                       ' me ',' you '),

               ' my ',' your '),

       ' I ',' You '),

' I''ve ',' You''ve '))

 FROM #poem

--which changes the meaning entirely!




STUFF is the Swiss army knife of string substitution. You can insert

any number of characters at a particular point in a string, with the

option of deleting existing characters at that point.

With apologies for repeating myself, here is a good example of the

use of STUFF, which inserts the ordinal suffix into a date. It is

difficult to do it as concisely any other way.*/


    DATENAME(dw,GETDATE())+', '

   + STUFF(CONVERT(CHAR(11),GETDATE(),106),3,0,


   'stndrdthththththththththththththththththstndrdthththththththst '


/*Thursday, 02nd Nov 2006

One can even use it for awkward operations like deleting part of the

string, as I will show later on in the article.

       Slicing Strings Up: LEFT RIGHT and SUBSTRING


There are three functions that are generally used for slicing strings

into substrings. These are LEFT, RIGHT and SUBSTRING. LEFT gives
however many characters you specify from the left, or start, of the

string and RIGHT gives however many characters you specify from the

right, or end, of the string. SUBSTRING works like LEFT but allows

you to specify the start position.

Here is another string-slicer based on using CHARINDEX, LEFT and

STUFF which, likes the previous example, slices a series of delimited

strings into a table.



CREATE   FUNCTION dbo.uftSecondSplitVarcharToTable


 @StringArray VARCHAR(8000),

 @Delimiter VARCHAR(10)



@Results TABLE


 SeqNo INT IDENTITY(1, 1), Item VARCHAR(8000)




DECLARE @Splitpoint INT

DECLARE @lenDelimiter INT

--initialise everything

SELECT @lenDelimiter=LEN(REPLACE(@Delimiter,' ','|'))

--notice we have to be cautious about LEN with trailing spaces!

--while there is more of the string



       SELECT @splitpoint=CHARINDEX(@Delimiter,@StringArray)

       IF @SplitPoint=0


               INSERT INTO @Results (Item) SELECT @StringArray



       INSERT INTO @Results (Item)

               SELECT LEFT(@StringArray,@Splitpoint-1)

       --use STUFF to delete the first x characters of the string!

       SELECT @StringArray=






--So we can use this routine to get a word frequency count of the


DECLARE @LongString VARCHAR(8000)

SELECT @LongString

              =COALESCE(@longString+' ','')+REPLACE(line,',','')+' '

       FROM #poem


       FROM dbo.uftSecondSplitVarcharToTable(@LongString,' ')

       WHERE item<> ''

       GROUP BY item

       ORDER BY COUNT(*),item DESC

/* RIGHT returns the rightmost characters of a string as with:    */

SELECT RIGHT('Robyn Page',4)




Just occasionally, the REPLICATE function is very handy, though

mainly in formatting fixed-width text. It creates a string, using

whatever character you specify, to whatever length you specify.

Here, we’ll demonstrate its use*/

SELECT '+'+REPLICATE('-',10)+'+'+CHAR(13)+CHAR(10)

       +REPLICATE('|'+REPLICATE(' ',10)+'|'+CHAR(13)+CHAR(10),8)



which draws a box! As an exercise, what about writing the poem within

a box?


|          |

|          |

|          |

|          |

|          |

|          |

|          |

|          |




SPACE(10) (return a string consisting of ten spaces) is equivalent to

REPLICATE(' ',10). The SPACE function just returns a string with

however many spaces you specify. It was more popular in the days of

printed reports on fixed-width fonts where the results had to be

printed in decimal point alignment, or right-aligned*/


SELECT SPACE(10-CHARINDEX('.',item+'.'))+item

FROM dbo.uftSecondSplitVarcharToTable(

















The REVERSE function, which merely returns the string backwards

execute this to discover the message...             */


'evil ot sah eh|hcihw ni|pmaws a ylno sa|nam a fo skniht|mreg a tub|

nem ot elbanoitcejbo|yrev era smreg'


/*REVERSE is occasionally very useful, and on those occasions

nothing else will do. In this example, we find the last occurrence of
a substring in a string and delete it*/









   [line]='There be no truth in that there be and that is what I say'


--which yields...

--There be no truth in that and that is what I say


        Changing case: LOWER and UPPER

There are two useful functions, LOWER and UPPER, which are pretty

SELECT UPPER('i have drunk too much caffeine'),

                                       LOWER('I MUST CALM DOWN')

/*To do capitalisation, you may want a function like this, which

shows a more complex use of UPPER



CREATE  FUNCTION [dbo].[ufsCapitalize]


@string VARCHAR(8000)








       --find word space followed by lower case letter

       --This makes assumptions about the language

       SELECT @next=


                       ' '+@string  collate Latin1_General_CS_AI)

       IF @next =0 BREAK

       SELECT @String =



RETURN @string



--so now we try it out…

SELECT dbo.ufsCapitalize('leonard j poops jnr')


which results in...

Leonard J Poops Jnr

       Removing leading or trailing spaces RTRIM & LTRIM


There are two functions that can be used to trim either the
leading spaced or trailing spaces from strings*/

SELECT LTRIM('     this has leading spaces, ')

                       +RTRIM('this has trailing spaces          ')

--or both!


       +LTRIM(RTRIM('    This string has spaces fore and aft    '))



       Fuzzy searches,  SOUNDEX and DIFFERENCE


For doing fuzzy searches, there are two functions based on the old

'soundex' algorithm These are of no more than historical interest

and they seem to be in there purely for historical reasons but I'd

be interested if anyone can point out a use for them. Even if they

worked in one language, which they don't, they aren't even

internationally valid.

The functions are SOUNDEX and DIFFERENCE



SELECT line FROM #poem WHERE DIFFERENCE(line,'I was')=4


--Manipulating TEXT and NTEXT


For the deprecated TEXT and NText datatype, there are a only a few

functions that will work with them. These are PATINDEX, TEXTVALID,


As these are either covered elsewhere, or too esoteric to be within

the scope of the workbench, I'd like to refer you to Book On Line,

which covers them very well

Some questions


1/ What happens when you assign a string to a Varchar variable whose

   length is shorter then that of the string

2/ When replicating from a SQL 2005 publisher to a SQL 2000

   subscriber, how is a nVarchar(MAX) mapped?

3/ How do you specify the sort order of strings?

4/ What is width-sensitivity in a collation?

5/ How would you, with one function, find the start of the first word

   in a string that starts with a lower case character.

6/ How might you go about decimal-aligning numbers in a fixed-width


7/ How might one go about stripping all text in brackets from a

   VARCHAR variable?

8/ What collation would be a good choice id you were writing a SQL

   Server Database that would be used in several European countries.



See Also



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