I have to increase group_concat_max_len. I cannot do it by preparestatement, and also I cannot do it in mysql my.conf file. I found on mysql docs that there is an option to pass session variables in url. But there is no example, I tried to do it like that: jdbc.url=jdbc:mysql://xxxx.xx.xx.xx/dbName?sessionVariables=group_concat_max_len:204800 and I have this exception: com.mysql.jdbc.exceptions.jd