Using CASE in WHERE Statement when parameter has multiple values

Question

I have a problem which I think relates to having a multiple value parameter.

In my TblActivity there are two fields TblActivity.ActivityServActId

Answer 1

If your @ServiceActivity is something like 1,2,3

You can do something like this

WHERE  `,1,2,3,` LIKE `%,1,%` 

So you format your variables

WHERE  ',' + @ServiceActivity + ',' LIKE '%,' + ID + ',%'

SQL FIDDLE DEMO

SELECT *
FROM 
    (SELECT '1,2,3,4' as X UNION ALL
     SELECT '2,3,4,5' as X UNION ALL
     SELECT '3,4,5,6' as X UNION ALL
     SELECT '1,3,4,5' as X 
     ) as T
WHERE ',' + X + ','  LIKE  '%,1,%'

For Your Case

(CASE WHEN @YESNOActivity = 'Yes' 
           THEN ',' + @ServiceActivity + ','
           ELSE NULL 
 END)
LIKE
(CASE WHEN @YESNOActivity = 'Yes' 
           THEN '%,' + TblActivity.ActivityServActId + ',%'
           ELSE 0 
 END)