Remove only leading or trailing carriage returns - sql

Question

I'm dumbfounded that this question has not been asked meaningfully already. How does one go about creating an equivalent function in SQL like LTRIM or RTRIM for carriage returns and line feeds ONLY at the start or end of a string.
Obviously REPLACE(REPLACE(#MyString,char(10),''),char(13),'') removes ALL carriage returns and new line feeds. Which is NOT what I'm looking for. I just want to remove leading or trailing ones.

Answer 1

Find the first character that is not CHAR(13) or CHAR(10) and subtract its position from the string's length.
LTRIM()
SELECT RIGHT(#MyString,LEN(#MyString)-PATINDEX('%[^'+CHAR(13)+CHAR(10)+']%',#MyString)+1)
RTRIM()
SELECT LEFT(#MyString,LEN(#MyString)-PATINDEX('%[^'+CHAR(13)+CHAR(10)+']%',REVERSE(#MyString))+1)

Answer 2

Following functions are enhanced types of trim functions you can use. Copied from sqlauthority.com
These functions remove trailing spaces, leading spaces, white space, tabs, carriage returns, line feeds etc.
Trim Left
CREATE FUNCTION dbo.LTrimX(#str VARCHAR(MAX)) RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE #trimchars VARCHAR(10)
SET #trimchars = CHAR(9)+CHAR(10)+CHAR(13)+CHAR(32)
IF #str LIKE '[' + #trimchars + ']%' SET #str = SUBSTRING(#str, PATINDEX('%[^' + #trimchars + ']%', #str), LEN(#str))
RETURN #str
END
Trim Right
CREATE FUNCTION dbo.RTrimX(#str VARCHAR(MAX)) RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE #trimchars VARCHAR(10)
SET #trimchars = CHAR(9)+CHAR(10)+CHAR(13)+CHAR(32)
IF #str LIKE '%[' + #trimchars + ']'
SET #str = REVERSE(dbo.LTrimX(REVERSE(#str)))
RETURN #str
END
Trim both Left and Right
CREATE FUNCTION dbo.TrimX(#str VARCHAR(MAX)) RETURNS VARCHAR(MAX)
AS
BEGIN
RETURN dbo.LTrimX(dbo.RTrimX(#str))
END
Using function
SELECT dbo.TRIMX(#MyString)
If you do use these functions you might also consider changing from varchar to nvarchar to support more encodings.

Answer 3

In SQL Server 2017 you can use the TRIM function to remove specific characters from beginning and end, in one go:
WITH testdata(str) AS (
SELECT CHAR(13) + CHAR(10) + ' test ' + CHAR(13) + CHAR(10)
)
SELECT
str,
TRIM(CHAR(13) + CHAR(10) + CHAR(9) + ' ' FROM str) AS [trim cr/lf/tab/space],
TRIM(CHAR(13) + CHAR(10) FROM str) AS [trim cr/lf],
TRIM(' ' FROM str) AS [trim space]
FROM testdata
Result:
Note that the last example (trim space) does nothing as expected since the spaces are in the middle.

Answer 4

Here's an example you may run:
I decided to cast the results as an Xml value, so when you click on it, you will be able to view the Carriage Returns.
DECLARE #CRLF Char(2) = (CHAR(0x0D) + CHAR(0x0A))
DECLARE #String VarChar(MAX) = #CRLF + #CRLF + ' Hello' + #CRLF + 'World ' + #CRLF + #CRLF
--Unmodified String:
SELECT CAST(#String as Xml)[Unmodified]
--Remove Trailing Whitespace (including Spaces).
SELECT CAST(LEFT(#String, LEN(REPLACE(#String, #CRLF, ' '))) as Xml)[RemoveTrailingWhitespace]
--Remove Leading Whitespace (including Spaces).
SELECT CAST(RIGHT(#String, LEN(REVERSE(REPLACE(#String, #CRLF, ' ')))) as Xml)[RemoveLeadingWhitespace]
--Remove Leading & Trailing Whitespace (including Spaces).
SELECT CAST(SUBSTRING(#String, LEN(REPLACE(#String, ' ', '_')) - LEN(REVERSE(REPLACE(#String, #CRLF, ' '))) + 1, LEN(LTRIM(RTRIM(REPLACE(#String, #CRLF, ' '))))) as Xml)[RemoveAllWhitespace]
--Remove Only Leading and Trailing CR/LF's (while still preserving all other Whitespace - including Spaces). - 04/06/2016 - MCR.
SELECT CAST(SUBSTRING(#String, PATINDEX('%[^'+CHAR(13)+CHAR(10)+']%',#String), LEN(REPLACE(#String, ' ', '_')) - PATINDEX('%[^'+CHAR(13)+CHAR(10)+']%',#String) + 1 - PATINDEX('%[^'+CHAR(13)+CHAR(10)+']%', REVERSE(#String)) + 1) as Xml)[RemoveLeadingAndTrailingCRLFsOnly]
Remember to remove the Cast-to-Xml, as this was done just as a Proof-of-Concept to show it works.
How is this better than the currently Accepted Answer?
At first glance this may appear to use more Functions than the Accepted Answer.
However, this is not the case.
If you combine both approaches listed in the Accepted Answer (to remove both Trailing and Leading whitespace), you will either have to make two passes updating the Record, or copy all of one Logic into the other (everywhere #String is listed), which would cause way more function calls and become even more difficult to read.

Answer 5

I was stuck using Microsoft SQL Server 2008 R2 and so basing my functions on #sqluser's answer I came up with the below. This will return an empty string if the string only contains the characters to be trimmed.
The bit that threw me was the pattern for PATINDEX must be included between % characters, which for a while I was thinking of as the same wildcard in a LIKE statement but which I now believe is just the syntax to denote a pattern, though I may be wrong!
CREATE FUNCTION [dbo].[ExtendedLTRIM](#string_to_trim VARCHAR(MAX))
RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE #tab CHAR(1) = CHAR(9);
DECLARE #line_feed CHAR(1) = CHAR(10);
DECLARE #carriage_return CHAR(1) = CHAR(13);
DECLARE #space CHAR(1) = CHAR(32);
DECLARE #characters_to_trim VARCHAR(10)
SET #characters_to_trim = #tab + #line_feed + #carriage_return + #space
IF #string_to_trim LIKE '[' + #characters_to_trim + ']%'
BEGIN
DECLARE #first_non_trim_character INT = PATINDEX('%[^' + #characters_to_trim + ']%', #string_to_trim);
IF #first_non_trim_character = 0 RETURN '';
RETURN SUBSTRING(#string_to_trim, #first_non_trim_character, 8000)
END
RETURN #string_to_trim
END
GO

Answer 6

To trim characters from a pre-defined list you'll want to create the following UDF (should work in 2008R2 and above).
Handles both sides in a single pass and doesn't care if it's a CRLF, LFCR (yep, seen that abomination more than once), bare LF or a bunch of spaces.
is easy to extend to e.g. add additional parameters to do LTRIM/RTRIM only, or a full purge (that last bit is simpler to do in 2017 by incorporating STRING_AGG, but perfectly doable in 2008R2); as a matter of fact this is a simplified version of something I use to do all those things. If anybody is interested then let me know and I'll update:
CREATE FUNCTION fnTrimHarder
(
#String VARCHAR(MAX)
)
RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE
#Start INT,
#Len INT,
#Chars CHAR(5) = CONCAT(
CHAR(9), -- TAB
CHAR(10), -- LF
CHAR(13), -- CR
' '
), -- List of invalid characters
#Return VARCHAR(MAX) = '';
IF #String NOT LIKE '%[^' + #Chars + ']%' -- If string contains only invalid characters
OR COALESCE(#String, '') = '' -- Optional addition for NULL handling
RETURN #Return
ELSE
BEGIN -- Create a "table" of characters with ordinals, calculate the start of string and its length, then return the substring
WITH CTE AS (
SELECT 1 AS n
UNION ALL
SELECT n + 1
FROM CTE
WHERE n < LEN(#String)
)
SELECT
#Start = MIN(n),
#Len = 1 + MAX(n) - MIN(n)
FROM CTE
WHERE SUBSTRING(#String, n, 1) NOT LIKE '[' + #Chars + ']';
SET #Return = SUBSTRING(#String, #Start, #Len)
END
RETURN #Return
END
GO