[syslog-ng]question about syslog-ng to MySQL

Hi all! I'm pretty new here in the hole syslog-ng world; so I have a litte question witch might sounds stupid for you... but any help would be great! I successfuly set up syslog-ng to log into the MySQL database. But now I want to filter the events before they are piped into the database (I don't want the logs from the cron jobs to be logged). Does anybody can tell me how I can achieve this?? Thanks in advance martin, switzerland