I want to create a JDBC Realm for my web app. Since my users are very different from each other i need to have just one table, with the usernames and passwords for the realm, i
I assume (from your previous question) that you don't have a group table. In fact you don't necessarily need one. JDBCRealm works with only a user table containing a group column as well.
In your Glassfish admin console change the following:
Group Table: Role
Group Name Column: userType
Since you used different typings (letter cases) for the word "role", make sure that the configuration values for your realm are exactly the same as in the table.