Here's the documentation for custom sql. I hope, it helps.

https://help.liferay.com/hc/en-us/articles/360017882012-Custom-SQL

When you write the code, you can add an Impl class that matches the table, in that example EntryImpl is used.

q.addEntity("GB_Entry", EntryImpl.class);

What I did before is was to add my own class that matched the result. I used the "dummy entity trick" by Dave Nebinger. It should still work.

https://liferay.dev/blogs/-/blogs/fake-servicebuilder-entities

But I think, doing that isn't strictly necessary, I think, any class works, as long as the column names match the setters/getters. But I could be wrong here.

.. The only thing I would add here is that the dummy entities got a little bit cleaner in 7.2 because you can now generate service builder entities without the persistence layer. So that means you don't have to worry about "disabling" the crud operations. All you have to do is make sure that you set the attribute persistence="false" on the <entity/> definition and Service Builder will do the rest .. or rather do LESS for you :)