Split and concatenate function

-- Split and concatenate back to string
CREATE FUNCTION [dbo].[Split_and_concatenate]
(
        @str NVARCHAR(MAX)
   ,@delimiter CHAR(1)
)
RETURNS NVARCHAR(MAX)
AS 
BEGIN

       
       DECLARE @pos INT = 0
       DECLARE @i INT = 1
       DECLARE @nextPos INT
       DECLARE @item NVARCHAR(4000)
       DECLARE @maxLen INT = LEN(@str)
       DECLARE @delim CHAR(1) 
       DECLARE @tableItem TABLE (
                                  value INT
                                 ,doSomething VARCHAR(50)
                                 ,GROUPBY CHAR(1)
                                )
       DECLARE @returnValues VARCHAR(500) 

   SET @delim = @delimiter

       WHILE @maxLen >= @pos
       BEGIN  
                SET @nextPos = CHARINDEX(@delimiter, @str, @pos);

                IF (@nextPos = 0 OR @nextPos IS NULL) 
                            SELECT @nextPos = @maxLen + 1;

                SET @item = LTRIM(RTRIM(SUBSTRING(@str, @pos, @nextPos - @pos)));
                    
                    INSERT INTO @tableItem
                    SELECT @item
/*  START: --- COPY/PASTE YOUR CASE STATEMENT --- */                           ,CASE 
                                  WHEN @item = 1 THEN '11'
                                  WHEN @item = 2 THEN '22' 
ELSE '33'
      
                             END
/*  END: --- COPY/PASTE YOUR CASE STATEMENT --- */                             ,1   AS GROUPBY 
                SET @pos = @nextPos+LEN(@delimiter)      
                SET @i = @i + 1

       END

       SELECT  @returnValues =
             SUBSTRING((SELECT '; '+ST1.doSomething  AS [text()]
                                  FROM 
@tableItem AS ST1
                                  WHERE 
ST1.GROUPBY = ST2.GROUPBY
                                  FOR XML PATH ('')),2, 10000) 
                 
 FROM @tableItem AS ST2


RETURN @returnValues

END;
GO


-- HOW TO USE Function
DECLARE @myString VARCHAR(10) = '1,1,2,2,42'
DECLARE @delimiter CHAR(1) = ','

SELECT
 @myString AS inputString
,[dbo].[Split_and_concatenate](@myString, @delimiter) AS outputString