Use variable for IN clause

So you mean that @excludeclasses could be something like a comma separated string?

set @excludeclasses = 'class1,class2,class3'

Then you can
1) create the parmstolist function attached below
2) use it in your delete query like this

DELETE  FROM bb_classes
    WHERE   ( AccountNo_FK = @AccountNo
              AND ClassName NOT IN (select [Value] from dbo.parmstolist(@ExludeClasses, ','))

create FUNCTION [dbo].[ParmsToList] (@Parameters varchar(8000), @delimiter varchar(10) ) 
returns @result TABLE (Value varchar(500), rn int identity) 
AS 
begin 
declare @dx varchar(9) 
-- declare @loops int 
--set @loops = 0 

DECLARE @TempList table 
( 
Value varchar(500) 
) 

if @delimiter is null set @delimiter = ' ' 
if len(@delimiter) < 1 set @delimiter = ' ' 
set @dx = left(@delimiter, case when @delimiter = ' ' then 1 else len(@delimiter) end -1) 

DECLARE @Value varchar(8000), @Pos int 

SET @Parameters = LTRIM(RTRIM(@Parameters))+ @delimiter 
SET @Pos = CHARINDEX(@delimiter, @Parameters, 1) 

IF REPLACE(@Parameters, @delimiter, @dx) <> '' 
BEGIN 
WHILE @Pos > 0 -- AND @Loops < 100 
BEGIN 
--set @loops = @loops + 1 
SET @Value = LTRIM(RTRIM(LEFT(@Parameters, @Pos - 1))) 
IF @Value <> '' 
BEGIN 
INSERT INTO @TempList (Value) VALUES (@Value) --Use Appropriate conversion 
END 
SET @Parameters = SUBSTRING(@Parameters, @Pos+ case when @delimiter = ' ' then 1 else len(@delimiter) end, 8000) 
SET @Pos = CHARINDEX(@delimiter, @Parameters, 1) 

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

Select allOpen in new window

IN works against a subquery (which requires a select statement) or a list.  In your case, surrounding the variable with a pair of single quotes may work.  For example,

DELETE  FROM bb_classes
    WHERE   ( AccountNo_FK = @AccountNo
              AND ClassName NOT IN ( '' + @ExludeClasses  + '')

Note, there is a typo in the variable name for this post (@ExludeClasses), which, I assume, you do not have in the actual query.

If you do not want to create a function as ralmada mentioned, try like this.

DELETE FROM bb_classes 
      WHERE (AccountNo_FK = @AccountNo 
             AND ClassName NOT IN (SELECT Ltrim(Substring(ExcludeClasses,n,Charindex(',',ExcludeClasses + ',',n) - n)) AS ExcludeClasses 
                                     FROM (SELECT @ExcludeClasses ExcludeClasses) AS t1 
                                          CROSS JOIN (SELECT NUMBER 
                                                        FROM MASTER..spt_values 
                                                       WHERE TYPE = 'P') AS Numbers(n) 
                                    WHERE Substring(',' + ExcludeClasses,n,1) = ',' 
                                          AND n < Len(ExcludeClasses) + 1))

Select allOpen in new window

I had written an article about that:
https://www.experts-exchange.com/A_1536.html

Splitting up strings using a separator is a fairly nasty solution - though until recently, was the only solution.  Instead, you can use the new User Defined Table Type (UDTT) that SQL Server 2008 provides.

Create the UDTT and stored proc:

CREATE TYPE [dbo].[udttClassName] AS TABLE(
      [ClassName] nvarchar(50) NOT NULL)
GO

CREATE PROCEDURE dbo.DeleteClasses(
    @AccountNo as varchar(20),
    @ExcludeClasses as udttClassName READONLY
)
AS
    DELETE FROM bb_classes
    WHERE AccountNo_FK = @AccountNo
      AND ClassName NOT IN (SELECT ClassName FROM @ExcludeClasses)

GO


Execute your stored proc this way:

DECLARE @ClassNames as udttClassName
INSERT INTO @ClassNames SELECT 'Class1' UNION
                        SELECT 'Class2'
                       
EXEC DeleteClasses '123', @ClassNames

VBisMe,
 
 the main issue is still the same: the input comes from the end-user, so you have to "split" the data (1 string) into several strings anyhow?

I don't see anywhere in the above requirement that he specified that he must use a comma separated string as a parameter for his stored procedure.  

On the flip side, if you want to pass a sring, then you don't need to split them at all.  You can simply perform a LIKE statement as follows.  Note: Start/End string commas are required to ensure the full ClassName is matched.

DELETE FROM bb_classes
WHERE AccountNo_FK = @AccountNo
  AND (',' + @ExcludeClasses + ',') NOT LIKE ('%,' + ClassName + ',%')


Personally, I'd use a UDTT.