this is a known problem that has already been fixed. You are probably using MySQL or MS SQL. Since we can not release an official build yet, we will start providing temporary beta/integration versions.
I think that by the end of the day, or tomorrow a build will be available here: https://sourceforge.net/projects/jasperstudio/files/beta-release/
The packages folder will contain the product files for the different platforms as usual.
The updatesite folder will contain the update site content for the plug-in version.
P.S: you can still enter the query manually how it was done in the previous versions of JSS (prior to 5.2.0). However please check the location later today or tomorrow, in order to have a temporary workaround.
I tried the version 5.6.0 of Jasperstudio, I use MySQL as the database, it is now possible to see the tables could not see before, but when making inquiries with this visual diagram puts quotes to sql language which marks Error since MySQL does not accept the SELECT field, field FROM table with the quotes and you need to remove them manually. Schedule an example:
as you can see put quotes and quotes should not take for MySQL.