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-- ufn_StrExtract ---
IF EXISTS (SELECT * FROM sysobjects WHERE  name = N'ufn_StrExtract')
	DROP FUNCTION ufn_StrExtract
GO

CREATE FUNCTION ufn_StrExtract (
	@StrIn varchar(8000),
	@StartDelim varchar(128),
	@EndDelim varchar(128),
	@Flag int=0)
									
RETURNS varchar(8000)
AS
/* Extracts part of a string between two delimiters
 Parameters:
	@StrIn  - source character expression 
	@StartDelim, @EndDelim - start and end delimiters
	@Flag - modifies function behavior:
			  2 - End delimiter not required. If it's not found returns the rest of the string
			  4 - Delimiters are included in result
*/
BEGIN
	DECLARE @StartPos int, @EndPos int, @LenStartDelim int, @LenEndDelim int
	DECLARE @StrOut varchar(8000)
	
	-- DATALENGTH() returns actual length including trailing spaces
	SET @LenStartDelim = DATALENGTH(@StartDelim)
	SET @LenEndDelim   = DATALENGTH(@EndDelim)

	IF @LenStartDelim = 0  
		-- If Start delimiter is empty, extract from the beginning of the string 
		SET @StartPos = 1
	ELSE
		-- Find Start delimiter position in the string
		SET @StartPos = CHARINDEX(@StartDelim, @StrIn)

	IF @StartPos > 0	BEGIN	
		-- Look for End delimiter position
		IF @LenEndDelim = 0  
			-- If End delimiter is empty, extract to the end of the string 
			SET @EndPos = DATALENGTH(@StrIn) 
		ELSE BEGIN
			-- Find End delimiter position in the string
			SET @EndPos = CHARINDEX(@EndDelim, @StrIn, @StartPos + 1) - 1
			IF (@EndPos <= 0) AND (@flag & 2)>0
				-- The End delimiter is not found but flag 2 is set
				--	extract to the end of the string	
				SET @EndPos = DATALENGTH(@StrIn) 
		END
	END	
	
	IF (@StartPos > 0) AND (@EndPos > 0) BEGIN
		-- We found both delimiters
		IF (@flag & 4)=0
			-- Flag 4 is not set, don't include Start delimiter into result
			SET @StartPos = @StartPos + @LenStartDelim
		IF @EndPos < DATALENGTH(@StrIn)  AND (@flag & 4)>0
			-- Flag 4 is set, include End delimiter into result
			SET @EndPos = @EndPos + @LenEndDelim
			
		-- Extract substring 
		SET @StrOut = SUBSTRING(@StrIn, @StartPos, @EndPos - @StartPos + 1)

	END
	ELSE
		-- One of the delimiters or both not found, return empty string
		SET @StrOut = ''

	RETURN @StrOut
END
GO

-- Sample of using ufn_StrExtract UDF
SELECT dbo.ufn_StrExtract('The quick brown fox jumps over the lazy dog', 'fox', 'dog', 4)
SELECT dbo.ufn_StrExtract('The quick brown fox jumps over the lazy dog', 'fox', 'dog', DEFAULT)