SQL - Stored Procedure with Select Statement using IN (@Variable_CommaDelimitedListOfIDS)

Since you're using SQL Server 2008, have a look at table-valued parameters.

For those cases I use this table function, which you can adapt to your needs:

CREATE FUNCTION dbo.f_params_to_list (@par VARCHAR(500))
returns @result TABLE (value VARCHAR(30))
AS  
begin
     DECLARE @TempList table
          (
          value VARCHAR(30)
          )

     DECLARE @Value varchar(30), @Pos int

     SET @par = LTRIM(RTRIM(@par))+ ','
     SET @Pos = CHARINDEX(',', @par, 1)

     IF REPLACE(@par, ',', '') <> ''
     BEGIN
          WHILE @Pos > 0
          BEGIN
               SET @Value = LTRIM(RTRIM(LEFT(@par, @Pos - 1)))
               IF @Value <> ''
               BEGIN
                    INSERT INTO @TempList (value) VALUES (@Value) --Use Appropriate conversion
               END
               SET @par = RIGHT(@par, LEN(@par) - @Pos)
               SET @Pos = CHARINDEX(',', @par, 1)

          END
     END    
     INSERT @result
     SELECT value 
        FROM @TempList
     RETURN
END    

In your stored procedure you would use it like this:

Create Procedure up_TEST
@Ids VARCHAR(MAX)
AS
SELECT * FROM ATable a
WHERE a.Id IN(SELECT value FROM dbo.f_params_to_list(@Ids))

Use a table values parameter (new in SQl Server 2008). Set it up by creating the actual table parameter type:

CREATE TYPE IntTableType AS TABLE (ID INTEGER PRIMARY KEY)

Your procedure would then be:

Create Procedure up_TEST
    @Ids IntTableType READONLY
AS

SELECT * 
    FROM ATable a
    WHERE a.Id IN (SELECT ID FROM @Ids)

RETURN 0
GO

if you can't use table value parameters, see: "Arrays and Lists in SQL Server 2008 Using Table-Valued Parameters" by Erland Sommarskog , then there are many ways to split string in SQL Server. This article covers the PROs and CONs of just about every method:

"Arrays and Lists in SQL Server 2005 and Beyond, When Table Value Parameters Do Not Cut it" by Erland Sommarskog

You need to create a split function. This is how a split function can be used:

SELECT
    *
    FROM YourTable                               y
    INNER JOIN dbo.yourSplitFunction(@Parameter) s ON y.ID=s.Value

I prefer the number table approach to split a string in TSQL but there are numerous ways to split strings in SQL Server, see the previous link, which explains the PROs and CONs of each.

For the Numbers Table method to work, you need to do this one time table setup, which will create a table Numbers that contains rows from 1 to 10,000:

SELECT TOP 10000 IDENTITY(int,1,1) AS Number
    INTO Numbers
    FROM sys.objects s1
    CROSS JOIN sys.objects s2
ALTER TABLE Numbers ADD CONSTRAINT PK_Numbers PRIMARY KEY CLUSTERED (Number)

Once the Numbers table is set up, create this split function:

CREATE FUNCTION [dbo].[FN_ListToTable]
(
     @SplitOn  char(1)      --REQUIRED, the character to split the @List string on
    ,@List     varchar(8000)--REQUIRED, the list to split apart
)
RETURNS TABLE
AS
RETURN 
(

    ----------------
    --SINGLE QUERY-- --this will not return empty rows
    ----------------
    SELECT
        ListValue
        FROM (SELECT
                  LTRIM(RTRIM(SUBSTRING(List2, number+1, CHARINDEX(@SplitOn, List2, number+1)-number - 1))) AS ListValue
                  FROM (
                           SELECT @SplitOn + @List + @SplitOn AS List2
                       ) AS dt
                      INNER JOIN Numbers n ON n.Number < LEN(dt.List2)
                  WHERE SUBSTRING(List2, number, 1) = @SplitOn
             ) dt2
        WHERE ListValue IS NOT NULL AND ListValue!=''

);
GO 

You can now easily split a CSV string into a table and join on it:

Create Procedure up_TEST
@Ids VARCHAR(MAX)
AS
SELECT * FROM ATable a
WHERE a.Id IN (SELECT ListValue FROM dbo.FN_ListToTable(',',@Ids))