How to observe output from query in Workbench 6.3?
Are there any records in table_A (not a good name by the way)? It should at least give you field names though.

For problems like this, it's always best to go back to the good-ol CLI (Command Line Interface) to make sure that nothing's wrong somewhere. 

You could also open a new Query (interactive) window and copy, paste and run your code and check that way.

As @MikeLischke points out, the system wasn't designed for interactive scripting in modelling mode (unsurprising really). 

However, when you open up MySQL Workbench, you have to choose the modelling option. You then get a new tab with that functionality. You can also open a new Query tab (File-> New Query tab...). You have to connect to an (already existing) schema to actually run any SQL (logically enough).

In the interests of fairness, I think you could maybe mark Mike's post as the correct answer (and give me a +1 if you think I deserve it! :-) ).