Converting comma separated string into table

From time to time I'm facing with trouble in SQL how to convert  comma separated string into table.
For instance, you may have set of comma delimited parameters that you want to use in select:
"'US','UA','RU','DE'"
You want to use this set of country codes to select clients.
Without converting the comma separated string into table you will have to use dynamic SQL:

  exec 'Select * from clients where Country in (' + @countryList + ')'

This solution is not very good because if you have request bigger then one line, its will be difficult to trace it in case of errors.

There is a small function that converts comma separated string into table:

CREATE FUNCTION [dbo].[fn_CommaSeparatedStringToTable] 
( 
    @CommaSeparatedValues     VARCHAR(MAX),
      @IncludeEmptyStrings    CHAR(1)
) 
RETURNS @Item TABLE  
( 
      RowId int IDENTITY(1, 1) NOT NULL,  
    Value VARCHAR(200) 
)
AS
BEGIN
      DECLARE @IndefOfComma int,@Value VARCHAR(200),@StartPos bigint,@EndPos bigint,@LengthOfString int, @ReachedEnd Char(1)
 

      SET @StartPos=1
      SET @EndPos=0
      SET @LengthOfString=LEN(@CommaSeparatedValues)
      SET @ReachedEnd='N'
 

      WHILE @ReachedEnd<>'Y'
            BEGIN
                  SET @EndPos=CHARINDEX(',',@CommaSeparatedValues,@StartPos) 
                  IF @EndPos>0
                  BEGIN
                      SET @Value = SUBSTRING(@CommaSeparatedValues, @StartPos,@EndPos-@StartPos)  
                      SET @StartPos=@EndPos+1       
                  END
                  ELSE
                  BEGIN
                     SEt @ReachedEnd='Y'
                     SET @Value = SUBSTRING(@CommaSeparatedValues, @StartPos,@LengthOfString-(@StartPos-1))
                  END
                  IF(@Value<>'' OR @IncludeEmptyStrings='Y')
                  INSERT INTO @Item(Value) VALUES(@Value)
      END
      RETURN
END

After using this function, you can use reqular sql queries:

    Select 
        * 
    from 
        clients c
        inner join dbo.fn_CommaSeparatedStringToTable(@countryList, 'N') t on t.Value = c.Country 

As you may see, this way is much more useful.