Problem with 'like' option in where clause in jasper 

Hi there 

I need to publish a report based on a sql query (mysql) that I am not allowed to modify.

The user has decided to use a column as a filter for the report. This column has multiple value options: concatenated results (value1,value2,value3) , single values or can even be null.

I have created a multi selected query and  a string parameter:

SELECT a.*
FROM 
(sql_query) AS a
WHERE
CASE WHEN $P(parameter) IS NULL THEN TRUE ELSE 
a.find_in_set($P(parameter), a.filter_column)

However I am not getting any result.

Im I doing something wrong, something is missing....

I would appreciate any answer you can give me.

Regards.