LSTR() and RSTR(): Enhanced LEFT() and RIGHT()

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Quite often I need to cut off the first (or last) few characters of a string. To do just that I created two functions LSTR() and RSTR().

Syntax: LSTR( @stringtocut, @length )
Note: @stringtocut is trimmed in the function

When @length is equal or larger than zero, this function performs the same as LEFT( LTRIM(RTRIM(@stringtocut)), @length ).
When @length is smaller than zero, it returns LTRIM(RTRIM(@stringtocut)) minus the right @length characters. 

Examples:
SET @ret = LSTR(' abcdef ',4) -> @ret = 'abcd'
SET @ret = LSTR(' abcdef ',0) -> @ret = ''
SET @ret = LSTR(' abcdef ',-4) -> @ret = 'ab'
SET @ret = LSTR(' abcdef ',9) -> @ret = 'abcdef'
SET @ret = LSTR(' abcdef ',-9) -> @ret = ''


Syntax: RSTR( @stringtocut, @length )
Examples:
SET @ret = RSTR(' abcdef ',4) -> @ret = 'cdef'
SET @ret = RSTR(' abcdef ',0) -> @ret = ''
SET @ret = RSTR(' abcdef ',-4) -> @ret = 'ef'
SET @ret = RSTR(' abcdef ',9) -> @ret = 'abcdef'
SET @ret = RSTR(' abcdef ',-9) -> @ret = ''

CREATE FUNCTION [dbo].[LSTR] (@str  VARCHAR(8000), @len INT)
RETURNS VARCHAR(8000)
AS
BEGIN
	SET @str = LTRIM(RTRIM(@str))
	RETURN(
		CASE WHEN @len=0 OR LEN(@str)+@len <= 0
			THEN ''
		ELSE
			CASE WHEN @len>0
				THEN LEFT(@str, @len)
			ELSE
				LEFT(@str, LEN(@str)+@len)
			END
		END
	)
END


CREATE FUNCTION [dbo].[RSTR] (@str VARCHAR(8000), @len INT)
RETURNS VARCHAR(8000)
AS
BEGIN
	SET @str = LTRIM(RTRIM(@str))
	RETURN(
		CASE WHEN @len=0 OR LEN(@str)+@len <= 0
			THEN ''
		ELSE
			CASE WHEN @len>0
				THEN RIGHT(@str, @len)
			ELSE
				RIGHT(@str, LEN(@str)+@len)
			END
		END
	)
END

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