SQL WHERE CLAUSE HELP NEEDED
===

I have a column in a table with sample data as follows:

    ServiceTypeIDs
    1,9
    4

In my Where clause I use the following to search on it:

       WHERE
    ( @ServiceTypes is null or       
       charindex(','+cast(SEP.ServiceTypeIDs as varchar(255))+',',      
       ','+@ServiceTypes+',') > 0)))

If my param @ServieTypes = '1,9' then I get results but when its i @ServiceTypes = '1' or just '9' then I dont recieve any thing back. Please help as im stuck and tried the above. thanks all